Stop running pub get at gclient sync time and fix build bugs

mojo/public/dart/third_party/analyzer/lib/src/generated/engine.dart

+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library engine;
+
+import 'dart:async';
+import 'dart:collection';
+import 'dart:math' as math;
+
+import 'package:analyzer/src/cancelable_future.dart';
+import 'package:analyzer/src/context/cache.dart' as cache;
+import 'package:analyzer/src/context/context.dart' as newContext;
+import 'package:analyzer/src/generated/incremental_resolution_validator.dart';
+import 'package:analyzer/src/plugin/command_line_plugin.dart';
+import 'package:analyzer/src/plugin/engine_plugin.dart';
+import 'package:analyzer/src/plugin/options_plugin.dart';
+import 'package:analyzer/src/services/lint.dart';
+import 'package:analyzer/src/task/manager.dart';
+import 'package:analyzer/task/dart.dart';
+import 'package:analyzer/task/model.dart';
+import 'package:html/dom.dart' show Document;
+import 'package:plugin/manager.dart';
+import 'package:plugin/plugin.dart';
+
+import '../../instrumentation/instrumentation.dart';
+import 'ast.dart';
+import 'constant.dart';
+import 'element.dart';
+import 'error.dart';
+import 'error_verifier.dart';
+import 'html.dart' as ht;
+import 'incremental_resolver.dart'
+    show IncrementalResolver, PoorMansIncrementalResolver;
+import 'incremental_scanner.dart';
+import 'java_core.dart';
+import 'java_engine.dart';
+import 'parser.dart' show Parser, IncrementalParser;
+import 'resolver.dart';
+import 'scanner.dart';
+import 'sdk.dart' show DartSdk;
+import 'source.dart';
+import 'utilities_collection.dart';
+import 'utilities_general.dart';
+
+/**
+ * Used by [AnalysisOptions] to allow function bodies to be analyzed in some
+ * sources but not others.
+ */
+typedef bool AnalyzeFunctionBodiesPredicate(Source source);
+
+/**
+ * Type of callback functions used by PendingFuture.  Functions of this type
+ * should perform a computation based on the data in [sourceEntry] and return
+ * it.  If the computation can't be performed yet because more analysis is
+ * needed, null should be returned.
+ *
+ * The function may also throw an exception, in which case the corresponding
+ * future will be completed with failure.
+ *
+ * Since this function is called while the state of analysis is being updated,
+ * it should be free of side effects so that it doesn't cause reentrant
+ * changes to the analysis state.
+ */
+typedef T PendingFutureComputer<T>(SourceEntry sourceEntry);
+
+/**
+ * An LRU cache of information related to analysis.
+ */
+class AnalysisCache {
+  /**
+   * A flag used to control whether trace information should be produced when
+   * the content of the cache is modified.
+   */
+  static bool _TRACE_CHANGES = false;
+
+  /**
+   * A list containing the partitions of which this cache is comprised.
+   */
+  final List<CachePartition> _partitions;
+
+  /**
+   * Initialize a newly created cache to have the given [_partitions]. The
+   * partitions will be searched in the order in which they appear in the list,
+   * so the most specific partition (usually an [SdkCachePartition]) should be
+   * first and the most general (usually a [UniversalCachePartition]) last.
+   */
+  AnalysisCache(this._partitions);
+
+  /**
+   * Return the number of entries in this cache that have an AST associated with
+   * them.
+   */
+  int get astSize => _partitions[_partitions.length - 1].astSize;
+
+  /**
+   * Return information about each of the partitions in this cache.
+   */
+  List<AnalysisContextStatistics_PartitionData> get partitionData {
+    int count = _partitions.length;
+    List<AnalysisContextStatistics_PartitionData> data =
+        new List<AnalysisContextStatistics_PartitionData>(count);
+    for (int i = 0; i < count; i++) {
+      CachePartition partition = _partitions[i];
+      data[i] = new AnalysisContextStatisticsImpl_PartitionDataImpl(
+          partition.astSize, partition.map.length);
+    }
+    return data;
+  }
+
+  /**
+   * Record that the AST associated with the given [source] was just read from
+   * the cache.
+   */
+  void accessedAst(Source source) {
+    int count = _partitions.length;
+    for (int i = 0; i < count; i++) {
+      if (_partitions[i].contains(source)) {
+        _partitions[i].accessedAst(source);
+        return;
+      }
+    }
+  }
+
+  /**
+   * Return the entry associated with the given [source].
+   */
+  SourceEntry get(Source source) {
+    int count = _partitions.length;
+    for (int i = 0; i < count; i++) {
+      if (_partitions[i].contains(source)) {
+        return _partitions[i].get(source);
+      }
+    }
+    //
+    // We should never get to this point because the last partition should
+    // always be a universal partition, except in the case of the SDK context,
+    // in which case the source should always be part of the SDK.
+    //
+    return null;
+  }
+
+  /**
+   * Return context that owns the given [source].
+   */
+  InternalAnalysisContext getContextFor(Source source) {
+    int count = _partitions.length;
+    for (int i = 0; i < count; i++) {
+      if (_partitions[i].contains(source)) {
+        return _partitions[i].context;
+      }
+    }
+    //
+    // We should never get to this point because the last partition should
+    // always be a universal partition, except in the case of the SDK context,
+    // in which case the source should always be part of the SDK.
+    //
+    AnalysisEngine.instance.logger.logInformation(
+        "Could not find context for ${source.fullName}",
+        new CaughtException(new AnalysisException(), null));
+    return null;
+  }
+
+  /**
+   * Return an iterator returning all of the map entries mapping sources to
+   * cache entries.
+   */
+  MapIterator<Source, SourceEntry> iterator() {
+    int count = _partitions.length;
+    List<Map<Source, SourceEntry>> maps =
+        new List<Map<Source, SourceEntry>>(count);
+    for (int i = 0; i < count; i++) {
+      maps[i] = _partitions[i].map;
+    }
+    return new MultipleMapIterator<Source, SourceEntry>(maps);
+  }
+
+  /**
+   * Associate the given [entry] with the given [source].
+   */
+  void put(Source source, SourceEntry entry) {
+    entry.fixExceptionState();
+    int count = _partitions.length;
+    for (int i = 0; i < count; i++) {
+      if (_partitions[i].contains(source)) {
+        if (_TRACE_CHANGES) {
+          try {
+            SourceEntry oldEntry = _partitions[i].get(source);
+            if (oldEntry == null) {
+              AnalysisEngine.instance.logger.logInformation(
+                  "Added a cache entry for '${source.fullName}'.");
+            } else {
+              AnalysisEngine.instance.logger.logInformation(
+                  "Modified the cache entry for ${source.fullName}'. Diff = ${entry.getDiff(oldEntry)}");
+            }
+          } catch (exception) {
+            // Ignored
+            JavaSystem.currentTimeMillis();
+          }
+        }
+        _partitions[i].put(source, entry);
+        return;
+      }
+    }
+  }
+
+  /**
+   * Remove all information related to the given [source] from this cache.
+   * Return the entry associated with the source, or `null` if there was cache
+   * entry for the source.
+   */
+  SourceEntry remove(Source source) {
+    int count = _partitions.length;
+    for (int i = 0; i < count; i++) {
+      if (_partitions[i].contains(source)) {
+        if (_TRACE_CHANGES) {
+          try {
+            AnalysisEngine.instance.logger.logInformation(
+                "Removed the cache entry for ${source.fullName}'.");
+          } catch (exception) {
+            // Ignored
+            JavaSystem.currentTimeMillis();
+          }
+        }
+        return _partitions[i].remove(source);
+      }
+    }
+    return null;
+  }
+
+  /**
+   * Record that the AST associated with the given [source] was just removed
+   * from the cache.
+   */
+  void removedAst(Source source) {
+    int count = _partitions.length;
+    for (int i = 0; i < count; i++) {
+      if (_partitions[i].contains(source)) {
+        _partitions[i].removedAst(source);
+        return;
+      }
+    }
+  }
+
+  /**
+   * Return the number of sources that are mapped to cache entries.
+   */
+  int size() {
+    int size = 0;
+    int count = _partitions.length;
+    for (int i = 0; i < count; i++) {
+      size += _partitions[i].size();
+    }
+    return size;
+  }
+
+  /**
+   * Record that the AST associated with the given [source] was just stored to
+   * the cache.
+   */
+  void storedAst(Source source) {
+    int count = _partitions.length;
+    for (int i = 0; i < count; i++) {
+      if (_partitions[i].contains(source)) {
+        _partitions[i].storedAst(source);
+        return;
+      }
+    }
+  }
+}
+
+/**
+ * A context in which a single analysis can be performed and incrementally
+ * maintained. The context includes such information as the version of the SDK
+ * being analyzed against as well as the package-root used to resolve 'package:'
+ * URI's. (Both of which are known indirectly through the [SourceFactory].)
+ *
+ * An analysis context also represents the state of the analysis, which includes
+ * knowing which sources have been included in the analysis (either directly or
+ * indirectly) and the results of the analysis. Sources must be added and
+ * removed from the context using the method [applyChanges], which is also used
+ * to notify the context when sources have been modified and, consequently,
+ * previously known results might have been invalidated.
+ *
+ * There are two ways to access the results of the analysis. The most common is
+ * to use one of the 'get' methods to access the results. The 'get' methods have
+ * the advantage that they will always return quickly, but have the disadvantage
+ * that if the results are not currently available they will return either
+ * nothing or in some cases an incomplete result. The second way to access
+ * results is by using one of the 'compute' methods. The 'compute' methods will
+ * always attempt to compute the requested results but might block the caller
+ * for a significant period of time.
+ *
+ * When results have been invalidated, have never been computed (as is the case
+ * for newly added sources), or have been removed from the cache, they are
+ * <b>not</b> automatically recreated. They will only be recreated if one of the
+ * 'compute' methods is invoked.
+ *
+ * However, this is not always acceptable. Some clients need to keep the
+ * analysis results up-to-date. For such clients there is a mechanism that
+ * allows them to incrementally perform needed analysis and get notified of the
+ * consequent changes to the analysis results. This mechanism is realized by the
+ * method [performAnalysisTask].
+ *
+ * Analysis engine allows for having more than one context. This can be used,
+ * for example, to perform one analysis based on the state of files on disk and
+ * a separate analysis based on the state of those files in open editors. It can
+ * also be used to perform an analysis based on a proposed future state, such as
+ * the state after a refactoring.
+ */
+abstract class AnalysisContext {
+  /**
+   * An empty list of contexts.
+   */
+  static const List<AnalysisContext> EMPTY_LIST = const <AnalysisContext>[];
+
+  /**
+   * Return the set of analysis options controlling the behavior of this
+   * context. Clients should not modify the returned set of options. The options
+   * should only be set by invoking the method [setAnalysisOptions].
+   */
+  AnalysisOptions get analysisOptions;
+
+  /**
+   * Set the set of analysis options controlling the behavior of this context to
+   * the given [options]. Clients can safely assume that all necessary analysis
+   * results have been invalidated.
+   */
+  void set analysisOptions(AnalysisOptions options);
+
+  /**
+   * Set the order in which sources will be analyzed by [performAnalysisTask] to
+   * match the order of the sources in the given list of [sources]. If a source
+   * that needs to be analyzed is not contained in the list, then it will be
+   * treated as if it were at the end of the list. If the list is empty (or
+   * `null`) then no sources will be given priority over other sources.
+   *
+   * Changes made to the list after this method returns will <b>not</b> be
+   * reflected in the priority order.
+   */
+  void set analysisPriorityOrder(List<Source> sources);
+
+  /**
+   * Return the set of declared variables used when computing constant values.
+   */
+  DeclaredVariables get declaredVariables;
+
+  /**
+   * Return a list containing all of the sources known to this context that
+   * represent HTML files. The contents of the list can be incomplete.
+   */
+  List<Source> get htmlSources;
+
+  /**
+   * The stream that is notified when a source either starts or stops being
+   * analyzed implicitly.
+   */
+  Stream<ImplicitAnalysisEvent> get implicitAnalysisEvents;
+
+  /**
+   * Returns `true` if this context was disposed using [dispose].
+   */
+  bool get isDisposed;
+
+  /**
+   * Return a list containing all of the sources known to this context that
+   * represent the defining compilation unit of a library that can be run within
+   * a browser. The sources that are returned represent libraries that have a
+   * 'main' method and are either referenced by an HTML file or import, directly
+   * or indirectly, a client-only library. The contents of the list can be
+   * incomplete.
+   */
+  List<Source> get launchableClientLibrarySources;
+
+  /**
+   * Return a list containing all of the sources known to this context that
+   * represent the defining compilation unit of a library that can be run
+   * outside of a browser. The contents of the list can be incomplete.
+   */
+  List<Source> get launchableServerLibrarySources;
+
+  /**
+   * Return a list containing all of the sources known to this context that
+   * represent the defining compilation unit of a library. The contents of the
+   * list can be incomplete.
+   */
+  List<Source> get librarySources;
+
+  /**
+   * Return a client-provided name used to identify this context, or `null` if
+   * the client has not provided a name.
+   */
+  String get name;
+
+  /**
+   * Set the client-provided name used to identify this context to the given
+   * [name].
+   */
+  set name(String name);
+
+  /**
+   * The stream that is notified when sources have been added or removed,
+   * or the source's content has changed.
+   */
+  Stream<SourcesChangedEvent> get onSourcesChanged;
+
+  /**
+   * Return the source factory used to create the sources that can be analyzed
+   * in this context.
+   */
+  SourceFactory get sourceFactory;
+
+  /**
+   * Set the source factory used to create the sources that can be analyzed in
+   * this context to the given source [factory]. Clients can safely assume that
+   * all analysis results have been invalidated.
+   */
+  void set sourceFactory(SourceFactory factory);
+
+  /**
+   * Return a list containing all of the sources known to this context.
+   */
+  List<Source> get sources;
+
+  /**
+   * Return a type provider for this context or throw [AnalysisException] if
+   * either `dart:core` or `dart:async` cannot be resolved.
+   */
+  TypeProvider get typeProvider;
+
+  /**
+   * Add the given [listener] to the list of objects that are to be notified
+   * when various analysis results are produced in this context.
+   */
+  void addListener(AnalysisListener listener);
+
+  /**
+   * Apply the given [delta] to change the level of analysis that will be
+   * performed for the sources known to this context.
+   */
+  void applyAnalysisDelta(AnalysisDelta delta);
+
+  /**
+   * Apply the changes specified by the given [changeSet] to this context. Any
+   * analysis results that have been invalidated by these changes will be
+   * removed.
+   */
+  void applyChanges(ChangeSet changeSet);
+
+  /**
+   * Return the documentation comment for the given [element] as it appears in
+   * the original source (complete with the beginning and ending delimiters) for
+   * block documentation comments, or lines starting with `"///"` and separated
+   * with `"\n"` characters for end-of-line documentation comments, or `null` if
+   * the element does not have a documentation comment associated with it. This
+   * can be a long-running operation if the information needed to access the
+   * comment is not cached.
+   *
+   * Throws an [AnalysisException] if the documentation comment could not be
+   * determined because the analysis could not be performed.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   */
+  String computeDocumentationComment(Element element);
+
+  /**
+   * Return a list containing all of the errors associated with the given
+   * [source]. If the errors are not already known then the source will be
+   * analyzed in order to determine the errors associated with it.
+   *
+   * Throws an [AnalysisException] if the errors could not be determined because
+   * the analysis could not be performed.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   *
+   * See [getErrors].
+   */
+  List<AnalysisError> computeErrors(Source source);
+
+  /**
+   * Return the element model corresponding to the HTML file defined by the
+   * given [source]. If the element model does not yet exist it will be created.
+   * The process of creating an element model for an HTML file can be
+   * long-running, depending on the size of the file and the number of libraries
+   * that are defined in it (via script tags) that also need to have a model
+   * built for them.
+   *
+   * Throws AnalysisException if the element model could not be determined
+   * because the analysis could not be performed.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   *
+   * See [getHtmlElement].
+   */
+  @deprecated
+  HtmlElement computeHtmlElement(Source source);
+
+  /**
+   * Return the kind of the given [source], computing it's kind if it is not
+   * already known. Return [SourceKind.UNKNOWN] if the source is not contained
+   * in this context.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   *
+   * See [getKindOf].
+   */
+  SourceKind computeKindOf(Source source);
+
+  /**
+   * Return the element model corresponding to the library defined by the given
+   * [source]. If the element model does not yet exist it will be created. The
+   * process of creating an element model for a library can long-running,
+   * depending on the size of the library and the number of libraries that are
+   * imported into it that also need to have a model built for them.
+   *
+   * Throws an [AnalysisException] if the element model could not be determined
+   * because the analysis could not be performed.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   *
+   * See [getLibraryElement].
+   */
+  LibraryElement computeLibraryElement(Source source);
+
+  /**
+   * Return the line information for the given [source], or `null` if the source
+   * is not of a recognized kind (neither a Dart nor HTML file). If the line
+   * information was not previously known it will be created. The line
+   * information is used to map offsets from the beginning of the source to line
+   * and column pairs.
+   *
+   * Throws an [AnalysisException] if the line information could not be
+   * determined because the analysis could not be performed.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   *
+   * See [getLineInfo].
+   */
+  LineInfo computeLineInfo(Source source);
+
+  /**
+   * Return a future which will be completed with the fully resolved AST for a
+   * single compilation unit within the given library, once that AST is up to
+   * date.
+   *
+   * If the resolved AST can't be computed for some reason, the future will be
+   * completed with an error.  One possible error is AnalysisNotScheduledError,
+   * which means that the resolved AST can't be computed because the given
+   * source file is not scheduled to be analyzed within the context of the
+   * given library.
+   */
+  CancelableFuture<CompilationUnit> computeResolvedCompilationUnitAsync(
+      Source source, Source librarySource);
+
+  /**
+   * Perform work until the given [result] has been computed for the given
+   * [target]. Return the computed value.
+   */
+  Object /*V*/ computeResult(AnalysisTarget target, ResultDescriptor /*<V>*/ result);
+
+  /**
+   * Notifies the context that the client is going to stop using this context.
+   */
+  void dispose();
+
+  /**
+   * Return `true` if the given [source] exists.
+   *
+   * This method should be used rather than the method [Source.exists] because
+   * contexts can have local overrides of the content of a source that the
+   * source is not aware of and a source with local content is considered to
+   * exist even if there is no file on disk.
+   */
+  bool exists(Source source);
+
+  /**
+   * Return the element model corresponding to the compilation unit defined by
+   * the given [unitSource] in the library defined by the given [librarySource],
+   * or `null` if the element model does not currently exist or if the library
+   * cannot be analyzed for some reason.
+   */
+  CompilationUnitElement getCompilationUnitElement(
+      Source unitSource, Source librarySource);
+
+  /**
+   * Return the contents and timestamp of the given [source].
+   *
+   * This method should be used rather than the method [Source.getContents]
+   * because contexts can have local overrides of the content of a source that
+   * the source is not aware of.
+   */
+  TimestampedData<String> getContents(Source source);
+
+  /**
+   * Return the element referenced by the given [location], or `null` if the
+   * element is not immediately available or if there is no element with the
+   * given location. The latter condition can occur, for example, if the
+   * location describes an element from a different context or if the element
+   * has been removed from this context as a result of some change since it was
+   * originally obtained.
+   */
+  Element getElement(ElementLocation location);
+
+  /**
+   * Return an analysis error info containing the list of all of the errors and
+   * the line info associated with the given [source]. The list of errors will
+   * be empty if the source is not known to this context or if there are no
+   * errors in the source. The errors contained in the list can be incomplete.
+   *
+   * See [computeErrors].
+   */
+  AnalysisErrorInfo getErrors(Source source);
+
+  /**
+   * Return the element model corresponding to the HTML file defined by the
+   * given [source], or `null` if the source does not represent an HTML file,
+   * the element representing the file has not yet been created, or the analysis
+   * of the HTML file failed for some reason.
+   *
+   * See [computeHtmlElement].
+   */
+  @deprecated
+  HtmlElement getHtmlElement(Source source);
+
+  /**
+   * Return the sources for the HTML files that reference the compilation unit
+   * with the given [source]. If the source does not represent a Dart source or
+   * is not known to this context, the returned list will be empty. The contents
+   * of the list can be incomplete.
+   */
+  List<Source> getHtmlFilesReferencing(Source source);
+
+  /**
+   * Return the kind of the given [source], or `null` if the kind is not known
+   * to this context.
+   *
+   * See [computeKindOf].
+   */
+  SourceKind getKindOf(Source source);
+
+  /**
+   * Return the sources for the defining compilation units of any libraries of
+   * which the given [source] is a part. The list will normally contain a single
+   * library because most Dart sources are only included in a single library,
+   * but it is possible to have a part that is contained in multiple identically
+   * named libraries. If the source represents the defining compilation unit of
+   * a library, then the returned list will contain the given source as its only
+   * element. If the source does not represent a Dart source or is not known to
+   * this context, the returned list will be empty. The contents of the list can
+   * be incomplete.
+   */
+  List<Source> getLibrariesContaining(Source source);
+
+  /**
+   * Return the sources for the defining compilation units of any libraries that
+   * depend on the library defined by the given [librarySource]. One library
+   * depends on another if it either imports or exports that library.
+   */
+  List<Source> getLibrariesDependingOn(Source librarySource);
+
+  /**
+   * Return the sources for the defining compilation units of any libraries that
+   * are referenced from the HTML file defined by the given [htmlSource].
+   */
+  List<Source> getLibrariesReferencedFromHtml(Source htmlSource);
+
+  /**
+   * Return the element model corresponding to the library defined by the given
+   * [source], or `null` if the element model does not currently exist or if the
+   * library cannot be analyzed for some reason.
+   */
+  LibraryElement getLibraryElement(Source source);
+
+  /**
+   * Return the line information for the given [source], or `null` if the line
+   * information is not known. The line information is used to map offsets from
+   * the beginning of the source to line and column pairs.
+   *
+   * See [computeLineInfo].
+   */
+  LineInfo getLineInfo(Source source);
+
+  /**
+   * Return the modification stamp for the [source], or a negative value if the
+   * source does not exist. A modification stamp is a non-negative integer with
+   * the property that if the contents of the source have not been modified
+   * since the last time the modification stamp was accessed then the same value
+   * will be returned, but if the contents of the source have been modified one
+   * or more times (even if the net change is zero) the stamps will be different.
+   *
+   * This method should be used rather than the method
+   * [Source.getModificationStamp] because contexts can have local overrides of
+   * the content of a source that the source is not aware of.
+   */
+  int getModificationStamp(Source source);
+
+  /**
+   * Return a fully resolved AST for the compilation unit defined by the given
+   * [unitSource] within the given [library], or `null` if the resolved AST is
+   * not already computed.
+   *
+   * See [resolveCompilationUnit].
+   */
+  CompilationUnit getResolvedCompilationUnit(
+      Source unitSource, LibraryElement library);
+
+  /**
+   * Return a fully resolved AST for the compilation unit defined by the given
+   * [unitSource] within the library defined by the given [librarySource], or
+   * `null` if the resolved AST is not already computed.
+   *
+   * See [resolveCompilationUnit2].
+   */
+  CompilationUnit getResolvedCompilationUnit2(
+      Source unitSource, Source librarySource);
+
+  /**
+   * Return the fully resolved HTML unit defined by the given [htmlSource], or
+   * `null` if the resolved unit is not already computed.
+   *
+   * See [resolveHtmlUnit].
+   */
+  @deprecated
+  ht.HtmlUnit getResolvedHtmlUnit(Source htmlSource);
+
+  /**
+   * Return the value of the given [result] for the given [target].
+   *
+   * If the corresponding [target] does not exist, or the [result] is not
+   * computed yet, then the default value is returned.
+   */
+  Object /*V*/ getResult(AnalysisTarget target, ResultDescriptor /*<V>*/ result);
+
+  /**
+   * Return a list of the sources being analyzed in this context whose full path
+   * is equal to the given [path].
+   */
+  List<Source> getSourcesWithFullName(String path);
+
+  /**
+   * Invalidates hints in the given [librarySource] and included parts.
+   */
+  void invalidateLibraryHints(Source librarySource);
+
+  /**
+   * Return `true` if the given [librarySource] is known to be the defining
+   * compilation unit of a library that can be run on a client (references
+   * 'dart:html', either directly or indirectly).
+   *
+   * <b>Note:</b> In addition to the expected case of returning `false` if the
+   * source is known to be a library that cannot be run on a client, this method
+   * will also return `false` if the source is not known to be a library or if
+   * we do not know whether it can be run on a client.
+   */
+  bool isClientLibrary(Source librarySource);
+
+  /**
+   * Return `true` if the given [librarySource] is known to be the defining
+   * compilation unit of a library that can be run on the server (does not
+   * reference 'dart:html', either directly or indirectly).
+   *
+   * <b>Note:</b> In addition to the expected case of returning `false` if the
+   * source is known to be a library that cannot be run on the server, this
+   * method will also return `false` if the source is not known to be a library
+   * or if we do not know whether it can be run on the server.
+   */
+  bool isServerLibrary(Source librarySource);
+
+  /**
+   * Return the stream that is notified when a new value for the given
+   * [descriptor] is computed.
+   */
+  Stream<ComputedResult> onResultComputed(ResultDescriptor descriptor);
+
+  /**
+   * Parse the content of the given [source] to produce an AST structure. The
+   * resulting AST structure may or may not be resolved, and may have a slightly
+   * different structure depending upon whether it is resolved.
+   *
+   * Throws an [AnalysisException] if the analysis could not be performed
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   */
+  CompilationUnit parseCompilationUnit(Source source);
+
+  /**
+   * Parse a single HTML [source] to produce a document model.
+   *
+   * Throws an [AnalysisException] if the analysis could not be performed
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   */
+  Document parseHtmlDocument(Source source);
+
+  /**
+   * Parse a single HTML [source] to produce an AST structure. The resulting
+   * HTML AST structure may or may not be resolved, and may have a slightly
+   * different structure depending upon whether it is resolved.
+   *
+   * Throws an [AnalysisException] if the analysis could not be performed
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   */
+  @deprecated // use parseHtmlDocument(source)
+  ht.HtmlUnit parseHtmlUnit(Source source);
+
+  /**
+   * Perform the next unit of work required to keep the analysis results
+   * up-to-date and return information about the consequent changes to the
+   * analysis results. This method can be long running.
+   *
+   * The implementation that uses the task model notifies subscribers of
+   * [onResultComputed] about computed results.
+   *
+   * The following results are computed for Dart sources.
+   *
+   * 1. For explicit and implicit sources:
+   *    [PARSED_UNIT]
+   *    [RESOLVED_UNIT]
+   *
+   * 2. For explicit sources:
+   *    [DART_ERRORS].
+   *
+   * 3. For explicit and implicit library sources:
+   *    [LIBRARY_ELEMENT].
+   */
+  AnalysisResult performAnalysisTask();
+
+  /**
+   * Remove the given [listener] from the list of objects that are to be
+   * notified when various analysis results are produced in this context.
+   */
+  void removeListener(AnalysisListener listener);
+
+  /**
+   * Return a fully resolved AST for the compilation unit defined by the given
+   * [unitSource] within the given [library].
+   *
+   * Throws an [AnalysisException] if the analysis could not be performed.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   *
+   * See [getResolvedCompilationUnit].
+   */
+  CompilationUnit resolveCompilationUnit(
+      Source unitSource, LibraryElement library);
+
+  /**
+   * Return a fully resolved AST for the compilation unit defined by the given
+   * [unitSource] within the library defined by the given [librarySource].
+   *
+   * Throws an [AnalysisException] if the analysis could not be performed.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   *
+   * See [getResolvedCompilationUnit2].
+   */
+  CompilationUnit resolveCompilationUnit2(
+      Source unitSource, Source librarySource);
+
+  /**
+   * Parse and resolve a single [htmlSource] within the given context to produce
+   * a fully resolved AST.
+   *
+   * Throws an [AnalysisException] if the analysis could not be performed.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   */
+  @deprecated
+  ht.HtmlUnit resolveHtmlUnit(Source htmlSource);
+
+  /**
+   * Set the contents of the given [source] to the given [contents] and mark the
+   * source as having changed. The additional [offset] and [length] information
+   * is used by the context to determine what reanalysis is necessary.
+   */
+  void setChangedContents(
+      Source source, String contents, int offset, int oldLength, int newLength);
+
+  /**
+   * Set the contents of the given [source] to the given [contents] and mark the
+   * source as having changed. This has the effect of overriding the default
+   * contents of the source. If the contents are `null` the override is removed
+   * so that the default contents will be returned.
+   */
+  void setContents(Source source, String contents);
+
+  /**
+   * Check the cache for any invalid entries (entries whose modification time
+   * does not match the modification time of the source associated with the
+   * entry). Invalid entries will be marked as invalid so that the source will
+   * be re-analyzed. Return `true` if at least one entry was invalid.
+   */
+  bool validateCacheConsistency();
+}
+
+/**
+ * An [AnalysisContext].
+ */
+class AnalysisContextImpl implements InternalAnalysisContext {
+  /**
+   * The difference between the maximum cache size and the maximum priority
+   * order size. The priority list must be capped so that it is less than the
+   * cache size. Failure to do so can result in an infinite loop in
+   * performAnalysisTask() because re-caching one AST structure can cause
+   * another priority source's AST structure to be flushed.
+   */
+  static int _PRIORITY_ORDER_SIZE_DELTA = 4;
+
+  /**
+   * A flag indicating whether trace output should be produced as analysis tasks
+   * are performed. Used for debugging.
+   */
+  static bool _TRACE_PERFORM_TASK = false;
+
+  /**
+   * The next context identifier.
+   */
+  static int _NEXT_ID = 0;
+
+  /**
+   * The unique identifier of this context.
+   */
+  final int _id = _NEXT_ID++;
+
+  /**
+   * A client-provided name used to identify this context, or `null` if the
+   * client has not provided a name.
+   */
+  String name;
+
+  /**
+   * The set of analysis options controlling the behavior of this context.
+   */
+  AnalysisOptionsImpl _options = new AnalysisOptionsImpl();
+
+  /**
+   * A flag indicating whether errors related to implicitly analyzed sources
+   * should be generated and reported.
+   */
+  bool _generateImplicitErrors = true;
+
+  /**
+   * A flag indicating whether errors related to sources in the SDK should be
+   * generated and reported.
+   */
+  bool _generateSdkErrors = true;
+
+  /**
+   * A flag indicating whether this context is disposed.
+   */
+  bool _disposed = false;
+
+  /**
+   * A cache of content used to override the default content of a source.
+   */
+  ContentCache _contentCache = new ContentCache();
+
+  /**
+   * The source factory used to create the sources that can be analyzed in this
+   * context.
+   */
+  SourceFactory _sourceFactory;
+
+  /**
+   * The set of declared variables used when computing constant values.
+   */
+  DeclaredVariables _declaredVariables = new DeclaredVariables();
+
+  /**
+   * A source representing the core library.
+   */
+  Source _coreLibrarySource;
+
+  /**
+   * A source representing the async library.
+   */
+  Source _asyncLibrarySource;
+
+  /**
+   * The partition that contains analysis results that are not shared with other
+   * contexts.
+   */
+  CachePartition _privatePartition;
+
+  /**
+   * A table mapping the sources known to the context to the information known
+   * about the source.
+   */
+  AnalysisCache _cache;
+
+  /**
+   * A list containing sources for which data should not be flushed.
+   */
+  List<Source> _priorityOrder = Source.EMPTY_LIST;
+
+  /**
+   * A map from all sources for which there are futures pending to a list of
+   * the corresponding PendingFuture objects.  These sources will be analyzed
+   * in the same way as priority sources, except with higher priority.
+   *
+   * TODO(paulberry): since the size of this map is not constrained (as it is
+   * for _priorityOrder), we run the risk of creating an analysis loop if
+   * re-caching one AST structure causes the AST structure for another source
+   * with pending futures to be flushed.  However, this is unlikely to happen
+   * in practice since sources are removed from this hash set as soon as their
+   * futures have completed.
+   */
+  HashMap<Source, List<PendingFuture>> _pendingFutureSources =
+      new HashMap<Source, List<PendingFuture>>();
+
+  /**
+   * A list containing sources whose AST structure is needed in order to resolve
+   * the next library to be resolved.
+   */
+  HashSet<Source> _neededForResolution = null;
+
+  /**
+   * A table mapping sources to the change notices that are waiting to be
+   * returned related to that source.
+   */
+  HashMap<Source, ChangeNoticeImpl> _pendingNotices =
+      new HashMap<Source, ChangeNoticeImpl>();
+
+  /**
+   * The object used to record the results of performing an analysis task.
+   */
+  AnalysisContextImpl_AnalysisTaskResultRecorder _resultRecorder;
+
+  /**
+   * Cached information used in incremental analysis or `null` if none.
+   */
+  IncrementalAnalysisCache _incrementalAnalysisCache;
+
+  /**
+   * The [TypeProvider] for this context, `null` if not yet created.
+   */
+  TypeProvider _typeProvider;
+
+  /**
+   * The object used to manage the list of sources that need to be analyzed.
+   */
+  WorkManager _workManager = new WorkManager();
+
+  /**
+   * The [Stopwatch] of the current "perform tasks cycle".
+   */
+  Stopwatch _performAnalysisTaskStopwatch;
+
+  /**
+   * The controller for sending [SourcesChangedEvent]s.
+   */
+  StreamController<SourcesChangedEvent> _onSourcesChangedController;
+
+  /**
+   * A subscription for a stream of events indicating when files are (and are
+   * not) being implicitly analyzed.
+   */
+  StreamController<ImplicitAnalysisEvent> _implicitAnalysisEventsController;
+
+  /**
+   * The listeners that are to be notified when various analysis results are
+   * produced in this context.
+   */
+  List<AnalysisListener> _listeners = new List<AnalysisListener>();
+
+  /**
+   * The most recently incrementally resolved source, or `null` when it was
+   * already validated, or the most recent change was not incrementally resolved.
+   */
+  Source incrementalResolutionValidation_lastUnitSource;
+
+  /**
+   * The most recently incrementally resolved library source, or `null` when it
+   * was already validated, or the most recent change was not incrementally
+   * resolved.
+   */
+  Source incrementalResolutionValidation_lastLibrarySource;
+
+  /**
+   * The result of incremental resolution result of
+   * [incrementalResolutionValidation_lastSource].
+   */
+  CompilationUnit incrementalResolutionValidation_lastUnit;
+
+  /**
+   * A factory to override how the [ResolverVisitor] is created.
+   */
+  ResolverVisitorFactory resolverVisitorFactory;
+
+  /**
+   * A factory to override how the [TypeResolverVisitor] is created.
+   */
+  TypeResolverVisitorFactory typeResolverVisitorFactory;
+
+  /**
+   * A factory to override how [LibraryResolver] is created.
+   */
+  LibraryResolverFactory libraryResolverFactory;
+
+  /**
+   * Initialize a newly created analysis context.
+   */
+  AnalysisContextImpl() {
+    _resultRecorder = new AnalysisContextImpl_AnalysisTaskResultRecorder(this);
+    _privatePartition = new UniversalCachePartition(
+        this,
+        AnalysisOptionsImpl.DEFAULT_CACHE_SIZE,
+        new AnalysisContextImpl_ContextRetentionPolicy(this));
+    _cache = createCacheFromSourceFactory(null);
+    _onSourcesChangedController =
+        new StreamController<SourcesChangedEvent>.broadcast();
+    _implicitAnalysisEventsController =
+        new StreamController<ImplicitAnalysisEvent>.broadcast();
+  }
+
+  @override
+  AnalysisCache get analysisCache => _cache;
+
+  @override
+  AnalysisOptions get analysisOptions => _options;
+
+  @override
+  void set analysisOptions(AnalysisOptions options) {
+    bool needsRecompute = this._options.analyzeFunctionBodiesPredicate !=
+            options.analyzeFunctionBodiesPredicate ||
+        this._options.generateImplicitErrors !=
+            options.generateImplicitErrors ||
+        this._options.generateSdkErrors != options.generateSdkErrors ||
+        this._options.dart2jsHint != options.dart2jsHint ||
+        (this._options.hint && !options.hint) ||
+        this._options.preserveComments != options.preserveComments ||
+        this._options.strongMode != options.strongMode ||
+        this._options.enableStrictCallChecks !=
+            options.enableStrictCallChecks ||
+        this._options.enableSuperMixins != options.enableSuperMixins;
+    int cacheSize = options.cacheSize;
+    if (this._options.cacheSize != cacheSize) {
+      this._options.cacheSize = cacheSize;
+      //cache.setMaxCacheSize(cacheSize);
+      _privatePartition.maxCacheSize = cacheSize;
+      //
+      // Cap the size of the priority list to being less than the cache size.
+      // Failure to do so can result in an infinite loop in
+      // performAnalysisTask() because re-caching one AST structure
+      // can cause another priority source's AST structure to be flushed.
+      //
+      // TODO(brianwilkerson) Remove this constraint when the new task model is
+      // implemented.
+      //
+      int maxPriorityOrderSize = cacheSize - _PRIORITY_ORDER_SIZE_DELTA;
+      if (_priorityOrder.length > maxPriorityOrderSize) {
+        _priorityOrder = _priorityOrder.sublist(0, maxPriorityOrderSize);
+      }
+    }
+    this._options.analyzeFunctionBodiesPredicate =
+        options.analyzeFunctionBodiesPredicate;
+    this._options.generateImplicitErrors = options.generateImplicitErrors;
+    this._options.generateSdkErrors = options.generateSdkErrors;
+    this._options.dart2jsHint = options.dart2jsHint;
+    this._options.enableStrictCallChecks = options.enableStrictCallChecks;
+    this._options.enableSuperMixins = options.enableSuperMixins;
+    this._options.hint = options.hint;
+    this._options.incremental = options.incremental;
+    this._options.incrementalApi = options.incrementalApi;
+    this._options.incrementalValidation = options.incrementalValidation;
+    this._options.lint = options.lint;
+    this._options.preserveComments = options.preserveComments;
+    this._options.strongMode = options.strongMode;
+    _generateImplicitErrors = options.generateImplicitErrors;
+    _generateSdkErrors = options.generateSdkErrors;
+    if (needsRecompute) {
+      _invalidateAllLocalResolutionInformation(false);
+    }
+  }
+
+  @override
+  void set analysisPriorityOrder(List<Source> sources) {
+    if (sources == null || sources.isEmpty) {
+      _priorityOrder = Source.EMPTY_LIST;
+    } else {
+      while (sources.remove(null)) {
+        // Nothing else to do.
+      }
+      if (sources.isEmpty) {
+        _priorityOrder = Source.EMPTY_LIST;
+      }
+      //
+      // Cap the size of the priority list to being less than the cache size.
+      // Failure to do so can result in an infinite loop in
+      // performAnalysisTask() because re-caching one AST structure
+      // can cause another priority source's AST structure to be flushed.
+      //
+      int count = math.min(
+          sources.length, _options.cacheSize - _PRIORITY_ORDER_SIZE_DELTA);
+      _priorityOrder = new List<Source>(count);
+      for (int i = 0; i < count; i++) {
+        _priorityOrder[i] = sources[i];
+      }
+      // Ensure entries for every priority source.
+      for (var source in _priorityOrder) {
+        SourceEntry entry = _getReadableSourceEntry(source);
+        if (entry == null) {
+          _createSourceEntry(source, false);
+        }
+      }
+    }
+  }
+
+  @override
+  set contentCache(ContentCache value) {
+    _contentCache = value;
+  }
+
+  @override
+  DeclaredVariables get declaredVariables => _declaredVariables;
+
+  @override
+  List<AnalysisTarget> get explicitTargets {
+    List<AnalysisTarget> targets = <AnalysisTarget>[];
+    MapIterator<Source, SourceEntry> iterator = _cache.iterator();
+    while (iterator.moveNext()) {
+      if (iterator.value.explicitlyAdded) {
+        targets.add(iterator.key);
+      }
+    }
+    return targets;
+  }
+
+  @override
+  List<Source> get htmlSources => _getSources(SourceKind.HTML);
+
+  @override
+  Stream<ImplicitAnalysisEvent> get implicitAnalysisEvents =>
+      _implicitAnalysisEventsController.stream;
+
+  @override
+  bool get isDisposed => _disposed;
+
+  @override
+  List<Source> get launchableClientLibrarySources {
+    // TODO(brianwilkerson) This needs to filter out libraries that do not
+    // reference dart:html, either directly or indirectly.
+    List<Source> sources = new List<Source>();
+    MapIterator<Source, SourceEntry> iterator = _cache.iterator();
+    while (iterator.moveNext()) {
+      Source source = iterator.key;
+      SourceEntry sourceEntry = iterator.value;
+      if (sourceEntry.kind == SourceKind.LIBRARY && !source.isInSystemLibrary) {
+//          DartEntry dartEntry = (DartEntry) sourceEntry;
+//          if (dartEntry.getValue(DartEntry.IS_LAUNCHABLE) && dartEntry.getValue(DartEntry.IS_CLIENT)) {
+        sources.add(source);
+//          }
+      }
+    }
+    return sources;
+  }
+
+  @override
+  List<Source> get launchableServerLibrarySources {
+    // TODO(brianwilkerson) This needs to filter out libraries that reference
+    // dart:html, either directly or indirectly.
+    List<Source> sources = new List<Source>();
+    MapIterator<Source, SourceEntry> iterator = _cache.iterator();
+    while (iterator.moveNext()) {
+      Source source = iterator.key;
+      SourceEntry sourceEntry = iterator.value;
+      if (sourceEntry.kind == SourceKind.LIBRARY && !source.isInSystemLibrary) {
+//          DartEntry dartEntry = (DartEntry) sourceEntry;
+//          if (dartEntry.getValue(DartEntry.IS_LAUNCHABLE) && !dartEntry.getValue(DartEntry.IS_CLIENT)) {
+        sources.add(source);
+//          }
+      }
+    }
+    return sources;
+  }
+
+  @override
+  List<Source> get librarySources => _getSources(SourceKind.LIBRARY);
+
+  /**
+   * Look through the cache for a task that needs to be performed. Return the
+   * task that was found, or `null` if there is no more work to be done.
+   */
+  AnalysisTask get nextAnalysisTask {
+    bool hintsEnabled = _options.hint;
+    bool lintsEnabled = _options.lint;
+    bool hasBlockedTask = false;
+    //
+    // Look for incremental analysis
+    //
+    if (_incrementalAnalysisCache != null &&
+        _incrementalAnalysisCache.hasWork) {
+      AnalysisTask task =
+          new IncrementalAnalysisTask(this, _incrementalAnalysisCache);
+      _incrementalAnalysisCache = null;
+      return task;
+    }
+    //
+    // Look for a source that needs to be analyzed because it has futures
+    // pending.
+    //
+    if (_pendingFutureSources.isNotEmpty) {
+      List<Source> sourcesToRemove = <Source>[];
+      AnalysisTask task;
+      for (Source source in _pendingFutureSources.keys) {
+        SourceEntry sourceEntry = _cache.get(source);
+        List<PendingFuture> pendingFutures = _pendingFutureSources[source];
+        for (int i = 0; i < pendingFutures.length;) {
+          if (pendingFutures[i].evaluate(sourceEntry)) {
+            pendingFutures.removeAt(i);
+          } else {
+            i++;
+          }
+        }
+        if (pendingFutures.isEmpty) {
+          sourcesToRemove.add(source);
+          continue;
+        }
+        AnalysisContextImpl_TaskData taskData = _getNextAnalysisTaskForSource(
+            source, sourceEntry, true, hintsEnabled, lintsEnabled);
+        task = taskData.task;
+        if (task != null) {
+          break;
+        } else if (taskData.isBlocked) {
+          hasBlockedTask = true;
+        } else {
+          // There is no more work to do for this task, so forcibly complete
+          // all its pending futures.
+          for (PendingFuture pendingFuture in pendingFutures) {
+            pendingFuture.forciblyComplete();
+          }
+          sourcesToRemove.add(source);
+        }
+      }
+      for (Source source in sourcesToRemove) {
+        _pendingFutureSources.remove(source);
+      }
+      if (task != null) {
+        return task;
+      }
+    }
+    //
+    // Look for a priority source that needs to be analyzed.
+    //
+    int priorityCount = _priorityOrder.length;
+    for (int i = 0; i < priorityCount; i++) {
+      Source source = _priorityOrder[i];
+      AnalysisContextImpl_TaskData taskData = _getNextAnalysisTaskForSource(
+          source, _cache.get(source), true, hintsEnabled, lintsEnabled);
+      AnalysisTask task = taskData.task;
+      if (task != null) {
+        return task;
+      } else if (taskData.isBlocked) {
+        hasBlockedTask = true;
+      }
+    }
+    if (_neededForResolution != null) {
+      List<Source> sourcesToRemove = new List<Source>();
+      for (Source source in _neededForResolution) {
+        SourceEntry sourceEntry = _cache.get(source);
+        if (sourceEntry is DartEntry) {
+          DartEntry dartEntry = sourceEntry;
+          if (!dartEntry.hasResolvableCompilationUnit) {
+            if (dartEntry.getState(DartEntry.PARSED_UNIT) == CacheState.ERROR) {
+              sourcesToRemove.add(source);
+            } else {
+              AnalysisContextImpl_TaskData taskData =
+                  _createParseDartTask(source, dartEntry);
+              AnalysisTask task = taskData.task;
+              if (task != null) {
+                return task;
+              } else if (taskData.isBlocked) {
+                hasBlockedTask = true;
+              }
+            }
+          }
+        }
+      }
+      int count = sourcesToRemove.length;
+      for (int i = 0; i < count; i++) {
+        _neededForResolution.remove(sourcesToRemove[i]);
+      }
+    }
+    //
+    // Look for a non-priority source that needs to be analyzed.
+    //
+    List<Source> sourcesToRemove = new List<Source>();
+    WorkManager_WorkIterator sources = _workManager.iterator();
+    try {
+      while (sources.hasNext) {
+        Source source = sources.next();
+        AnalysisContextImpl_TaskData taskData = _getNextAnalysisTaskForSource(
+            source, _cache.get(source), false, hintsEnabled, lintsEnabled);
+        AnalysisTask task = taskData.task;
+        if (task != null) {
+          return task;
+        } else if (taskData.isBlocked) {
+          hasBlockedTask = true;
+        } else {
+          sourcesToRemove.add(source);
+        }
+      }
+    } finally {
+      int count = sourcesToRemove.length;
+      for (int i = 0; i < count; i++) {
+        _workManager.remove(sourcesToRemove[i]);
+      }
+    }
+    if (hasBlockedTask) {
+      // All of the analysis work is blocked waiting for an asynchronous task
+      // to complete.
+      return WaitForAsyncTask.instance;
+    }
+    return null;
+  }
+
+  @override
+  Stream<SourcesChangedEvent> get onSourcesChanged =>
+      _onSourcesChangedController.stream;
+
+  /**
+   * Make _pendingFutureSources available to unit tests.
+   */
+  HashMap<Source, List<PendingFuture>> get pendingFutureSources_forTesting =>
+      _pendingFutureSources;
+
+  @override
+  List<Source> get prioritySources => _priorityOrder;
+
+  @override
+  List<AnalysisTarget> get priorityTargets => prioritySources;
+
+  @override
+  CachePartition get privateAnalysisCachePartition => _privatePartition;
+
+  @override
+  SourceFactory get sourceFactory => _sourceFactory;
+
+  @override
+  void set sourceFactory(SourceFactory factory) {
+    if (identical(_sourceFactory, factory)) {
+      return;
+    } else if (factory.context != null) {
+      throw new IllegalStateException(
+          "Source factories cannot be shared between contexts");
+    }
+    if (_sourceFactory != null) {
+      _sourceFactory.context = null;
+    }
+    factory.context = this;
+    _sourceFactory = factory;
+    _coreLibrarySource = _sourceFactory.forUri(DartSdk.DART_CORE);
+    _asyncLibrarySource = _sourceFactory.forUri(DartSdk.DART_ASYNC);
+    _cache = createCacheFromSourceFactory(factory);
+    _invalidateAllLocalResolutionInformation(true);
+  }
+
+  @override
+  List<Source> get sources {
+    List<Source> sources = new List<Source>();
+    MapIterator<Source, SourceEntry> iterator = _cache.iterator();
+    while (iterator.moveNext()) {
+      sources.add(iterator.key);
+    }
+    return sources;
+  }
+
+  /**
+   * Return a list of the sources that would be processed by
+   * [performAnalysisTask]. This method duplicates, and must therefore be kept
+   * in sync with, [getNextAnalysisTask]. This method is intended to be used for
+   * testing purposes only.
+   */
+  List<Source> get sourcesNeedingProcessing {
+    HashSet<Source> sources = new HashSet<Source>();
+    bool hintsEnabled = _options.hint;
+    bool lintsEnabled = _options.lint;
+
+    //
+    // Look for priority sources that need to be analyzed.
+    //
+    for (Source source in _priorityOrder) {
+      _getSourcesNeedingProcessing(source, _cache.get(source), true,
+          hintsEnabled, lintsEnabled, sources);
+    }
+    //
+    // Look for non-priority sources that need to be analyzed.
+    //
+    WorkManager_WorkIterator iterator = _workManager.iterator();
+    while (iterator.hasNext) {
+      Source source = iterator.next();
+      _getSourcesNeedingProcessing(source, _cache.get(source), false,
+          hintsEnabled, lintsEnabled, sources);
+    }
+    return new List<Source>.from(sources);
+  }
+
+  @override
+  AnalysisContextStatistics get statistics {
+    AnalysisContextStatisticsImpl statistics =
+        new AnalysisContextStatisticsImpl();
+    visitCacheItems(statistics._internalPutCacheItem);
+    statistics.partitionData = _cache.partitionData;
+    return statistics;
+  }
+
+  IncrementalAnalysisCache get test_incrementalAnalysisCache {
+    return _incrementalAnalysisCache;
+  }
+
+  set test_incrementalAnalysisCache(IncrementalAnalysisCache value) {
+    _incrementalAnalysisCache = value;
+  }
+
+  List<Source> get test_priorityOrder => _priorityOrder;
+
+  @override
+  TypeProvider get typeProvider {
+    if (_typeProvider != null) {
+      return _typeProvider;
+    }
+    Source coreSource = sourceFactory.forUri(DartSdk.DART_CORE);
+    if (coreSource == null) {
+      throw new AnalysisException("Could not create a source for dart:core");
+    }
+    LibraryElement coreElement = computeLibraryElement(coreSource);
+    if (coreElement == null) {
+      throw new AnalysisException("Could not create an element for dart:core");
+    }
+    Source asyncSource = sourceFactory.forUri(DartSdk.DART_ASYNC);
+    if (asyncSource == null) {
+      throw new AnalysisException("Could not create a source for dart:async");
+    }
+    LibraryElement asyncElement = computeLibraryElement(asyncSource);
+    if (asyncElement == null) {
+      throw new AnalysisException("Could not create an element for dart:async");
+    }
+    _typeProvider = new TypeProviderImpl(coreElement, asyncElement);
+    return _typeProvider;
+  }
+
+  /**
+   * Sets the [TypeProvider] for this context.
+   */
+  void set typeProvider(TypeProvider typeProvider) {
+    _typeProvider = typeProvider;
+  }
+
+  @override
+  void addListener(AnalysisListener listener) {
+    if (!_listeners.contains(listener)) {
+      _listeners.add(listener);
+    }
+  }
+
+  @override
+  void applyAnalysisDelta(AnalysisDelta delta) {
+    ChangeSet changeSet = new ChangeSet();
+    delta.analysisLevels.forEach((Source source, AnalysisLevel level) {
+      if (level == AnalysisLevel.NONE) {
+        changeSet.removedSource(source);
+      } else {
+        changeSet.addedSource(source);
+      }
+    });
+    applyChanges(changeSet);
+  }
+
+  @override
+  void applyChanges(ChangeSet changeSet) {
+    if (changeSet.isEmpty) {
+      return;
+    }
+    //
+    // First, compute the list of sources that have been removed.
+    //
+    List<Source> removedSources =
+        new List<Source>.from(changeSet.removedSources);
+    for (SourceContainer container in changeSet.removedContainers) {
+      _addSourcesInContainer(removedSources, container);
+    }
+    //
+    // Then determine which cached results are no longer valid.
+    //
+    for (Source source in changeSet.addedSources) {
+      _sourceAvailable(source);
+    }
+    for (Source source in changeSet.changedSources) {
+      if (_contentCache.getContents(source) != null) {
+        // This source is overridden in the content cache, so the change will
+        // have no effect. Just ignore it to avoid wasting time doing
+        // re-analysis.
+        continue;
+      }
+      _sourceChanged(source);
+    }
+    changeSet.changedContents.forEach((Source key, String value) {
+      _contentsChanged(key, value, false);
+    });
+    changeSet.changedRanges
+        .forEach((Source source, ChangeSet_ContentChange change) {
+      _contentRangeChanged(source, change.contents, change.offset,
+          change.oldLength, change.newLength);
+    });
+    for (Source source in changeSet.deletedSources) {
+      _sourceDeleted(source);
+    }
+    for (Source source in removedSources) {
+      _sourceRemoved(source);
+    }
+    _onSourcesChangedController.add(new SourcesChangedEvent(changeSet));
+  }
+
+  @override
+  String computeDocumentationComment(Element element) {
+    if (element == null) {
+      return null;
+    }
+    Source source = element.source;
+    if (source == null) {
+      return null;
+    }
+    CompilationUnit unit = parseCompilationUnit(source);
+    if (unit == null) {
+      return null;
+    }
+    NodeLocator locator = new NodeLocator(element.nameOffset);
+    AstNode nameNode = locator.searchWithin(unit);
+    while (nameNode != null) {
+      if (nameNode is AnnotatedNode) {
+        Comment comment = nameNode.documentationComment;
+        if (comment == null) {
+          return null;
+        }
+        StringBuffer buffer = new StringBuffer();
+        List<Token> tokens = comment.tokens;
+        for (int i = 0; i < tokens.length; i++) {
+          if (i > 0) {
+            buffer.write("\n");
+          }
+          buffer.write(tokens[i].lexeme);
+        }
+        return buffer.toString();
+      }
+      nameNode = nameNode.parent;
+    }
+    return null;
+  }
+
+  @override
+  List<AnalysisError> computeErrors(Source source) {
+    bool enableHints = _options.hint;
+    bool enableLints = _options.lint;
+
+    SourceEntry sourceEntry = _getReadableSourceEntry(source);
+    if (sourceEntry is DartEntry) {
+      List<AnalysisError> errors = new List<AnalysisError>();
+      try {
+        DartEntry dartEntry = sourceEntry;
+        ListUtilities.addAll(
+            errors, _getDartScanData(source, dartEntry, DartEntry.SCAN_ERRORS));
+        dartEntry = _getReadableDartEntry(source);
+        ListUtilities.addAll(errors,
+            _getDartParseData(source, dartEntry, DartEntry.PARSE_ERRORS));
+        dartEntry = _getReadableDartEntry(source);
+        if (dartEntry.getValue(DartEntry.SOURCE_KIND) == SourceKind.LIBRARY) {
+          ListUtilities.addAll(
+              errors,
+              _getDartResolutionData(
+                  source, source, dartEntry, DartEntry.RESOLUTION_ERRORS));
+          dartEntry = _getReadableDartEntry(source);
+          ListUtilities.addAll(
+              errors,
+              _getDartVerificationData(
+                  source, source, dartEntry, DartEntry.VERIFICATION_ERRORS));
+          if (enableHints) {
+            dartEntry = _getReadableDartEntry(source);
+            ListUtilities.addAll(errors,
+                _getDartHintData(source, source, dartEntry, DartEntry.HINTS));
+          }
+          if (enableLints) {
+            dartEntry = _getReadableDartEntry(source);
+            ListUtilities.addAll(errors,
+                _getDartLintData(source, source, dartEntry, DartEntry.LINTS));
+          }
+        } else {
+          List<Source> libraries = getLibrariesContaining(source);
+          for (Source librarySource in libraries) {
+            ListUtilities.addAll(
+                errors,
+                _getDartResolutionData(source, librarySource, dartEntry,
+                    DartEntry.RESOLUTION_ERRORS));
+            dartEntry = _getReadableDartEntry(source);
+            ListUtilities.addAll(
+                errors,
+                _getDartVerificationData(source, librarySource, dartEntry,
+                    DartEntry.VERIFICATION_ERRORS));
+            if (enableHints) {
+              dartEntry = _getReadableDartEntry(source);
+              ListUtilities.addAll(
+                  errors,
+                  _getDartHintData(
+                      source, librarySource, dartEntry, DartEntry.HINTS));
+            }
+            if (enableLints) {
+              dartEntry = _getReadableDartEntry(source);
+              ListUtilities.addAll(
+                  errors,
+                  _getDartLintData(
+                      source, librarySource, dartEntry, DartEntry.LINTS));
+            }
+          }
+        }
+      } on ObsoleteSourceAnalysisException catch (exception, stackTrace) {
+        AnalysisEngine.instance.logger.logInformation(
+            "Could not compute errors",
+            new CaughtException(exception, stackTrace));
+      }
+      if (errors.isEmpty) {
+        return AnalysisError.NO_ERRORS;
+      }
+      return errors;
+    } else if (sourceEntry is HtmlEntry) {
+      HtmlEntry htmlEntry = sourceEntry;
+      try {
+        return _getHtmlResolutionData2(
+            source, htmlEntry, HtmlEntry.RESOLUTION_ERRORS);
+      } on ObsoleteSourceAnalysisException catch (exception, stackTrace) {
+        AnalysisEngine.instance.logger.logInformation(
+            "Could not compute errors",
+            new CaughtException(exception, stackTrace));
+      }
+    }
+    return AnalysisError.NO_ERRORS;
+  }
+
+  @override
+  List<Source> computeExportedLibraries(Source source) => _getDartParseData2(
+      source, DartEntry.EXPORTED_LIBRARIES, Source.EMPTY_LIST);
+
+  @override
+  @deprecated
+  HtmlElement computeHtmlElement(Source source) =>
+      _getHtmlResolutionData(source, HtmlEntry.ELEMENT, null);
+
+  @override
+  List<Source> computeImportedLibraries(Source source) => _getDartParseData2(
+      source, DartEntry.IMPORTED_LIBRARIES, Source.EMPTY_LIST);
+
+  @override
+  SourceKind computeKindOf(Source source) {
+    SourceEntry sourceEntry = _getReadableSourceEntry(source);
+    if (sourceEntry == null) {
+      return SourceKind.UNKNOWN;
+    } else if (sourceEntry is DartEntry) {
+      try {
+        return _getDartParseData(source, sourceEntry, DartEntry.SOURCE_KIND);
+      } on AnalysisException {
+        return SourceKind.UNKNOWN;
+      }
+    }
+    return sourceEntry.kind;
+  }
+
+  @override
+  LibraryElement computeLibraryElement(Source source) =>
+      _getDartResolutionData2(source, source, DartEntry.ELEMENT, null);
+
+  @override
+  LineInfo computeLineInfo(Source source) {
+    SourceEntry sourceEntry = _getReadableSourceEntry(source);
+    try {
+      if (sourceEntry is HtmlEntry) {
+        return _getHtmlParseData(source, SourceEntry.LINE_INFO, null);
+      } else if (sourceEntry is DartEntry) {
+        return _getDartScanData2(source, SourceEntry.LINE_INFO, null);
+      }
+    } on ObsoleteSourceAnalysisException catch (exception, stackTrace) {
+      AnalysisEngine.instance.logger.logInformation(
+          "Could not compute ${SourceEntry.LINE_INFO}",
+          new CaughtException(exception, stackTrace));
+    }
+    return null;
+  }
+
+  @override
+  CompilationUnit computeResolvableCompilationUnit(Source source) {
+    DartEntry dartEntry = _getReadableDartEntry(source);
+    if (dartEntry == null) {
+      throw new AnalysisException(
+          "computeResolvableCompilationUnit for non-Dart: ${source.fullName}");
+    }
+    dartEntry = _cacheDartParseData(source, dartEntry, DartEntry.PARSED_UNIT);
+    CompilationUnit unit = dartEntry.resolvableCompilationUnit;
+    if (unit == null) {
+      throw new AnalysisException(
+          "Internal error: computeResolvableCompilationUnit could not parse ${source.fullName}",
+          new CaughtException(dartEntry.exception, null));
+    }
+    return unit;
+  }
+
+  @override
+  CancelableFuture<CompilationUnit> computeResolvedCompilationUnitAsync(
+      Source unitSource, Source librarySource) {
+    return new _AnalysisFutureHelper<CompilationUnit>(this)
+        .computeAsync(unitSource, (SourceEntry sourceEntry) {
+      if (sourceEntry is DartEntry) {
+        if (sourceEntry.getStateInLibrary(
+                DartEntry.RESOLVED_UNIT, librarySource) ==
+            CacheState.ERROR) {
+          throw sourceEntry.exception;
+        }
+        return sourceEntry.getValueInLibrary(
+            DartEntry.RESOLVED_UNIT, librarySource);
+      }
+      throw new AnalysisNotScheduledError();
+    });
+  }
+
+  @override
+  Object computeResult(AnalysisTarget target, ResultDescriptor result) {
+    return result.defaultValue;
+  }
+
+  /**
+   * Create an analysis cache based on the given source [factory].
+   */
+  AnalysisCache createCacheFromSourceFactory(SourceFactory factory) {
+    if (factory == null) {
+      return new AnalysisCache(<CachePartition>[_privatePartition]);
+    }
+    DartSdk sdk = factory.dartSdk;
+    if (sdk == null) {
+      return new AnalysisCache(<CachePartition>[_privatePartition]);
+    }
+    return new AnalysisCache(<CachePartition>[
+      AnalysisEngine.instance.partitionManager.forSdk(sdk),
+      _privatePartition
+    ]);
+  }
+
+  @override
+  void dispose() {
+    _disposed = true;
+    for (List<PendingFuture> pendingFutures in _pendingFutureSources.values) {
+      for (PendingFuture pendingFuture in pendingFutures) {
+        pendingFuture.forciblyComplete();
+      }
+    }
+    _pendingFutureSources.clear();
+  }
+
+  @override
+  List<CompilationUnit> ensureResolvedDartUnits(Source unitSource) {
+    SourceEntry sourceEntry = _cache.get(unitSource);
+    if (sourceEntry is! DartEntry) {
+      return null;
+    }
+    DartEntry dartEntry = sourceEntry;
+    // Check every library.
+    List<CompilationUnit> units = <CompilationUnit>[];
+    List<Source> containingLibraries = dartEntry.containingLibraries;
+    for (Source librarySource in containingLibraries) {
+      CompilationUnit unit =
+          dartEntry.getValueInLibrary(DartEntry.RESOLVED_UNIT, librarySource);
+      if (unit == null) {
+        units = null;
+        break;
+      }
+      units.add(unit);
+    }
+    // Invalidate the flushed RESOLVED_UNIT to force it eventually.
+    if (units == null) {
+      bool shouldBeScheduled = false;
+      for (Source librarySource in containingLibraries) {
+        if (dartEntry.getStateInLibrary(
+                DartEntry.RESOLVED_UNIT, librarySource) ==
+            CacheState.FLUSHED) {
+          dartEntry.setStateInLibrary(
+              DartEntry.RESOLVED_UNIT, librarySource, CacheState.INVALID);
+          shouldBeScheduled = true;
+        }
+      }
+      if (shouldBeScheduled) {
+        _workManager.add(unitSource, SourcePriority.UNKNOWN);
+      }
+      // We cannot provide resolved units right now,
+      // but the future analysis will.
+      return null;
+    }
+    // done
+    return units;
+  }
+
+  @override
+  bool exists(Source source) {
+    if (source == null) {
+      return false;
+    }
+    if (_contentCache.getContents(source) != null) {
+      return true;
+    }
+    return source.exists();
+  }
+
+  @override
+  cache.CacheEntry getCacheEntry(AnalysisTarget target) {
+    return null;
+  }
+
+  @override
+  CompilationUnitElement getCompilationUnitElement(
+      Source unitSource, Source librarySource) {
+    LibraryElement libraryElement = getLibraryElement(librarySource);
+    if (libraryElement != null) {
+      // try defining unit
+      CompilationUnitElement definingUnit =
+          libraryElement.definingCompilationUnit;
+      if (definingUnit.source == unitSource) {
+        return definingUnit;
+      }
+      // try parts
+      for (CompilationUnitElement partUnit in libraryElement.parts) {
+        if (partUnit.source == unitSource) {
+          return partUnit;
+        }
+      }
+    }
+    return null;
+  }
+
+  @override
+  TimestampedData<String> getContents(Source source) {
+    String contents = _contentCache.getContents(source);
+    if (contents != null) {
+      return new TimestampedData<String>(
+          _contentCache.getModificationStamp(source), contents);
+    }
+    return source.contents;
+  }
+
+  @override
+  InternalAnalysisContext getContextFor(Source source) {
+    InternalAnalysisContext context = _cache.getContextFor(source);
+    return context == null ? this : context;
+  }
+
+  @override
+  Element getElement(ElementLocation location) {
+    // TODO(brianwilkerson) This should not be a "get" method.
+    try {
+      List<String> components = location.components;
+      Source source = _computeSourceFromEncoding(components[0]);
+      String sourceName = source.shortName;
+      if (AnalysisEngine.isDartFileName(sourceName)) {
+        ElementImpl element = computeLibraryElement(source) as ElementImpl;
+        for (int i = 1; i < components.length; i++) {
+          if (element == null) {
+            return null;
+          }
+          element = element.getChild(components[i]);
+        }
+        return element;
+      }
+      if (AnalysisEngine.isHtmlFileName(sourceName)) {
+        return computeHtmlElement(source);
+      }
+    } catch (exception) {
+      // If the location cannot be decoded for some reason then the underlying
+      // cause should have been logged already and we can fall though to return
+      // null.
+    }
+    return null;
+  }
+
+  @override
+  AnalysisErrorInfo getErrors(Source source) {
+    SourceEntry sourceEntry = getReadableSourceEntryOrNull(source);
+    if (sourceEntry is DartEntry) {
+      DartEntry dartEntry = sourceEntry;
+      return new AnalysisErrorInfoImpl(
+          dartEntry.allErrors, dartEntry.getValue(SourceEntry.LINE_INFO));
+    } else if (sourceEntry is HtmlEntry) {
+      HtmlEntry htmlEntry = sourceEntry;
+      return new AnalysisErrorInfoImpl(
+          htmlEntry.allErrors, htmlEntry.getValue(SourceEntry.LINE_INFO));
+    }
+    return new AnalysisErrorInfoImpl(AnalysisError.NO_ERRORS, null);
+  }
+
+  @override
+  @deprecated
+  HtmlElement getHtmlElement(Source source) {
+    SourceEntry sourceEntry = getReadableSourceEntryOrNull(source);
+    if (sourceEntry is HtmlEntry) {
+      return sourceEntry.getValue(HtmlEntry.ELEMENT);
+    }
+    return null;
+  }
+
+  @override
+  List<Source> getHtmlFilesReferencing(Source source) {
+    SourceKind sourceKind = getKindOf(source);
+    if (sourceKind == null) {
+      return Source.EMPTY_LIST;
+    }
+    List<Source> htmlSources = new List<Source>();
+    while (true) {
+      if (sourceKind == SourceKind.PART) {
+        List<Source> librarySources = getLibrariesContaining(source);
+        MapIterator<Source, SourceEntry> partIterator = _cache.iterator();
+        while (partIterator.moveNext()) {
+          SourceEntry sourceEntry = partIterator.value;
+          if (sourceEntry.kind == SourceKind.HTML) {
+            List<Source> referencedLibraries = (sourceEntry as HtmlEntry)
+                .getValue(HtmlEntry.REFERENCED_LIBRARIES);
+            if (_containsAny(referencedLibraries, librarySources)) {
+              htmlSources.add(partIterator.key);
+            }
+          }
+        }
+      } else {
+        MapIterator<Source, SourceEntry> iterator = _cache.iterator();
+        while (iterator.moveNext()) {
+          SourceEntry sourceEntry = iterator.value;
+          if (sourceEntry.kind == SourceKind.HTML) {
+            List<Source> referencedLibraries = (sourceEntry as HtmlEntry)
+                .getValue(HtmlEntry.REFERENCED_LIBRARIES);
+            if (_contains(referencedLibraries, source)) {
+              htmlSources.add(iterator.key);
+            }
+          }
+        }
+      }
+      break;
+    }
+    if (htmlSources.isEmpty) {
+      return Source.EMPTY_LIST;
+    }
+    return htmlSources;
+  }
+
+  @override
+  SourceKind getKindOf(Source source) {
+    SourceEntry sourceEntry = getReadableSourceEntryOrNull(source);
+    if (sourceEntry == null) {
+      return SourceKind.UNKNOWN;
+    }
+    return sourceEntry.kind;
+  }
+
+  @override
+  List<Source> getLibrariesContaining(Source source) {
+    SourceEntry sourceEntry = getReadableSourceEntryOrNull(source);
+    if (sourceEntry is DartEntry) {
+      return sourceEntry.containingLibraries;
+    }
+    return Source.EMPTY_LIST;
+  }
+
+  @override
+  List<Source> getLibrariesDependingOn(Source librarySource) {
+    List<Source> dependentLibraries = new List<Source>();
+    MapIterator<Source, SourceEntry> iterator = _cache.iterator();
+    while (iterator.moveNext()) {
+      SourceEntry sourceEntry = iterator.value;
+      if (sourceEntry.kind == SourceKind.LIBRARY) {
+        if (_contains(
+            (sourceEntry as DartEntry).getValue(DartEntry.EXPORTED_LIBRARIES),
+            librarySource)) {
+          dependentLibraries.add(iterator.key);
+        }
+        if (_contains(
+            (sourceEntry as DartEntry).getValue(DartEntry.IMPORTED_LIBRARIES),
+            librarySource)) {
+          dependentLibraries.add(iterator.key);
+        }
+      }
+    }
+    if (dependentLibraries.isEmpty) {
+      return Source.EMPTY_LIST;
+    }
+    return dependentLibraries;
+  }
+
+  @override
+  List<Source> getLibrariesReferencedFromHtml(Source htmlSource) {
+    SourceEntry sourceEntry = getReadableSourceEntryOrNull(htmlSource);
+    if (sourceEntry is HtmlEntry) {
+      HtmlEntry htmlEntry = sourceEntry;
+      return htmlEntry.getValue(HtmlEntry.REFERENCED_LIBRARIES);
+    }
+    return Source.EMPTY_LIST;
+  }
+
+  @override
+  LibraryElement getLibraryElement(Source source) {
+    SourceEntry sourceEntry = getReadableSourceEntryOrNull(source);
+    if (sourceEntry is DartEntry) {
+      return sourceEntry.getValue(DartEntry.ELEMENT);
+    }
+    return null;
+  }
+
+  @override
+  LineInfo getLineInfo(Source source) {
+    SourceEntry sourceEntry = getReadableSourceEntryOrNull(source);
+    if (sourceEntry != null) {
+      return sourceEntry.getValue(SourceEntry.LINE_INFO);
+    }
+    return null;
+  }
+
+  @override
+  int getModificationStamp(Source source) {
+    int stamp = _contentCache.getModificationStamp(source);
+    if (stamp != null) {
+      return stamp;
+    }
+    return source.modificationStamp;
+  }
+
+  @override
+  ChangeNoticeImpl getNotice(Source source) {
+    ChangeNoticeImpl notice = _pendingNotices[source];
+    if (notice == null) {
+      notice = new ChangeNoticeImpl(source);
+      _pendingNotices[source] = notice;
+    }
+    return notice;
+  }
+
+  @override
+  Namespace getPublicNamespace(LibraryElement library) {
+    // TODO(brianwilkerson) Rename this to not start with 'get'.
+    // Note that this is not part of the API of the interface.
+    Source source = library.definingCompilationUnit.source;
+    DartEntry dartEntry = _getReadableDartEntry(source);
+    if (dartEntry == null) {
+      return null;
+    }
+    Namespace namespace = null;
+    if (identical(dartEntry.getValue(DartEntry.ELEMENT), library)) {
+      namespace = dartEntry.getValue(DartEntry.PUBLIC_NAMESPACE);
+    }
+    if (namespace == null) {
+      NamespaceBuilder builder = new NamespaceBuilder();
+      namespace = builder.createPublicNamespaceForLibrary(library);
+      if (dartEntry == null) {
+        AnalysisEngine.instance.logger.logError(
+            "Could not compute the public namespace for ${library.source.fullName}",
+            new CaughtException(
+                new AnalysisException(
+                    "A Dart file became a non-Dart file: ${source.fullName}"),
+                null));
+        return null;
+      }
+      if (identical(dartEntry.getValue(DartEntry.ELEMENT), library)) {
+        dartEntry.setValue(DartEntry.PUBLIC_NAMESPACE, namespace);
+      }
+    }
+    return namespace;
+  }
+
+  /**
+   * Return the cache entry associated with the given [source], or `null` if
+   * there is no entry associated with the source.
+   */
+  SourceEntry getReadableSourceEntryOrNull(Source source) => _cache.get(source);
+
+  @override
+  CompilationUnit getResolvedCompilationUnit(
+      Source unitSource, LibraryElement library) {
+    if (library == null) {
+      return null;
+    }
+    return getResolvedCompilationUnit2(unitSource, library.source);
+  }
+
+  @override
+  CompilationUnit getResolvedCompilationUnit2(
+      Source unitSource, Source librarySource) {
+    SourceEntry sourceEntry = getReadableSourceEntryOrNull(unitSource);
+    if (sourceEntry is DartEntry) {
+      return sourceEntry.getValueInLibrary(
+          DartEntry.RESOLVED_UNIT, librarySource);
+    }
+    return null;
+  }
+
+  @override
+  @deprecated
+  ht.HtmlUnit getResolvedHtmlUnit(Source htmlSource) {
+    SourceEntry sourceEntry = getReadableSourceEntryOrNull(htmlSource);
+    if (sourceEntry is HtmlEntry) {
+      HtmlEntry htmlEntry = sourceEntry;
+      return htmlEntry.getValue(HtmlEntry.RESOLVED_UNIT);
+    }
+    return null;
+  }
+
+  @override
+  Object getResult(AnalysisTarget target, ResultDescriptor result) {
+    return result.defaultValue;
+  }
+
+  @override
+  List<Source> getSourcesWithFullName(String path) {
+    List<Source> sources = <Source>[];
+    MapIterator<Source, SourceEntry> iterator = _cache.iterator();
+    while (iterator.moveNext()) {
+      if (iterator.key.fullName == path) {
+        sources.add(iterator.key);
+      }
+    }
+    return sources;
+  }
+
+  @override
+  bool handleContentsChanged(
+      Source source, String originalContents, String newContents, bool notify) {
+    SourceEntry sourceEntry = _cache.get(source);
+    if (sourceEntry == null) {
+      return false;
+    }
+    bool changed = newContents != originalContents;
+    if (newContents != null) {
+      if (changed) {
+        _incrementalAnalysisCache =
+            IncrementalAnalysisCache.clear(_incrementalAnalysisCache, source);
+        if (!analysisOptions.incremental ||
+            !_tryPoorMansIncrementalResolution(source, newContents)) {
+          _sourceChanged(source);
+        }
+        sourceEntry.modificationTime =
+            _contentCache.getModificationStamp(source);
+        sourceEntry.setValue(SourceEntry.CONTENT, newContents);
+      } else {
+        sourceEntry.modificationTime =
+            _contentCache.getModificationStamp(source);
+      }
+    } else if (originalContents != null) {
+      _incrementalAnalysisCache =
+          IncrementalAnalysisCache.clear(_incrementalAnalysisCache, source);
+      // We are removing the overlay for the file, check if the file's
+      // contents is the same as it was in the overlay.
+      try {
+        TimestampedData<String> fileContents = getContents(source);
+        newContents = fileContents.data;
+        sourceEntry.modificationTime = fileContents.modificationTime;
+        if (newContents == originalContents) {
+          sourceEntry.setValue(SourceEntry.CONTENT, newContents);
+          changed = false;
+        }
+      } catch (e) {}
+      // If not the same content (e.g. the file is being closed without save),
+      // then force analysis.
+      if (changed) {
+        if (!analysisOptions.incremental ||
+            !_tryPoorMansIncrementalResolution(source, newContents)) {
+          _sourceChanged(source);
+        }
+      }
+    }
+    if (notify && changed) {
+      _onSourcesChangedController
+          .add(new SourcesChangedEvent.changedContent(source, newContents));
+    }
+    return changed;
+  }
+
+  @override
+  void invalidateLibraryHints(Source librarySource) {
+    SourceEntry sourceEntry = _cache.get(librarySource);
+    if (sourceEntry is! DartEntry) {
+      return;
+    }
+    DartEntry dartEntry = sourceEntry;
+    // Prepare sources to invalidate hints in.
+    List<Source> sources = <Source>[librarySource];
+    sources.addAll(dartEntry.getValue(DartEntry.INCLUDED_PARTS));
+    // Invalidate hints and lints.
+    for (Source source in sources) {
+      DartEntry dartEntry = _cache.get(source);
+      if (dartEntry.getStateInLibrary(DartEntry.HINTS, librarySource) ==
+          CacheState.VALID) {
+        dartEntry.setStateInLibrary(
+            DartEntry.HINTS, librarySource, CacheState.INVALID);
+      }
+      if (dartEntry.getStateInLibrary(DartEntry.LINTS, librarySource) ==
+          CacheState.VALID) {
+        dartEntry.setStateInLibrary(
+            DartEntry.LINTS, librarySource, CacheState.INVALID);
+      }
+    }
+  }
+
+  @override
+  bool isClientLibrary(Source librarySource) {
+    SourceEntry sourceEntry = _getReadableSourceEntry(librarySource);
+    if (sourceEntry is DartEntry) {
+      DartEntry dartEntry = sourceEntry;
+      return dartEntry.getValue(DartEntry.IS_CLIENT) &&
+          dartEntry.getValue(DartEntry.IS_LAUNCHABLE);
+    }
+    return false;
+  }
+
+  @override
+  bool isServerLibrary(Source librarySource) {
+    SourceEntry sourceEntry = _getReadableSourceEntry(librarySource);
+    if (sourceEntry is DartEntry) {
+      DartEntry dartEntry = sourceEntry;
+      return !dartEntry.getValue(DartEntry.IS_CLIENT) &&
+          dartEntry.getValue(DartEntry.IS_LAUNCHABLE);
+    }
+    return false;
+  }
+
+  @override
+  Stream<ComputedResult> onResultComputed(ResultDescriptor descriptor) {
+    throw new NotImplementedException('In not task-based AnalysisContext.');
+  }
+
+  @override
+  CompilationUnit parseCompilationUnit(Source source) =>
+      _getDartParseData2(source, DartEntry.PARSED_UNIT, null);
+
+  @override
+  Document parseHtmlDocument(Source source) {
+    return null;
+  }
+
+  @override
+  @deprecated
+  ht.HtmlUnit parseHtmlUnit(Source source) =>
+      _getHtmlParseData(source, HtmlEntry.PARSED_UNIT, null);
+
+  @override
+  AnalysisResult performAnalysisTask() {
+    if (_TRACE_PERFORM_TASK) {
+      print("----------------------------------------");
+    }
+    return PerformanceStatistics.performAnaysis.makeCurrentWhile(() {
+      int getStart = JavaSystem.currentTimeMillis();
+      AnalysisTask task = PerformanceStatistics.nextTask
+          .makeCurrentWhile(() => nextAnalysisTask);
+      int getEnd = JavaSystem.currentTimeMillis();
+      if (task == null) {
+        _validateLastIncrementalResolutionResult();
+        if (_performAnalysisTaskStopwatch != null) {
+          AnalysisEngine.instance.instrumentationService.logPerformance(
+              AnalysisPerformanceKind.FULL,
+              _performAnalysisTaskStopwatch,
+              'context_id=$_id');
+          _performAnalysisTaskStopwatch = null;
+        }
+        return new AnalysisResult(
+            _getChangeNotices(true), getEnd - getStart, null, -1);
+      }
+      if (_performAnalysisTaskStopwatch == null) {
+        _performAnalysisTaskStopwatch = new Stopwatch()..start();
+      }
+      String taskDescription = task.toString();
+      _notifyAboutToPerformTask(taskDescription);
+      if (_TRACE_PERFORM_TASK) {
+        print(taskDescription);
+      }
+      int performStart = JavaSystem.currentTimeMillis();
+      try {
+        task.perform(_resultRecorder);
+      } on ObsoleteSourceAnalysisException catch (exception, stackTrace) {
+        AnalysisEngine.instance.logger.logInformation(
+            "Could not perform analysis task: $taskDescription",
+            new CaughtException(exception, stackTrace));
+      } on AnalysisException catch (exception, stackTrace) {
+        if (exception.cause is! JavaIOException) {
+          AnalysisEngine.instance.logger.logError(
+              "Internal error while performing the task: $task",
+              new CaughtException(exception, stackTrace));
+        }
+      }
+      int performEnd = JavaSystem.currentTimeMillis();
+      List<ChangeNotice> notices = _getChangeNotices(false);
+      int noticeCount = notices.length;
+      for (int i = 0; i < noticeCount; i++) {
+        ChangeNotice notice = notices[i];
+        Source source = notice.source;
+        // TODO(brianwilkerson) Figure out whether the compilation unit is
+        // always resolved, or whether we need to decide whether to invoke the
+        // "parsed" or "resolved" method. This might be better done when
+        // recording task results in order to reduce the chance of errors.
+//        if (notice.getCompilationUnit() != null) {
+//          notifyResolvedDart(source, notice.getCompilationUnit());
+//        } else if (notice.getHtmlUnit() != null) {
+//          notifyResolvedHtml(source, notice.getHtmlUnit());
+//        }
+        _notifyErrors(source, notice.errors, notice.lineInfo);
+      }
+      return new AnalysisResult(notices, getEnd - getStart,
+          task.runtimeType.toString(), performEnd - performStart);
+    });
+  }
+
+  @override
+  void recordLibraryElements(Map<Source, LibraryElement> elementMap) {
+    Source htmlSource = _sourceFactory.forUri(DartSdk.DART_HTML);
+    elementMap.forEach((Source librarySource, LibraryElement library) {
+      //
+      // Cache the element in the library's info.
+      //
+      DartEntry dartEntry = _getReadableDartEntry(librarySource);
+      if (dartEntry != null) {
+        _recordElementData(dartEntry, library, library.source, htmlSource);
+        dartEntry.setState(SourceEntry.CONTENT, CacheState.FLUSHED);
+        dartEntry.setValue(SourceEntry.LINE_INFO, new LineInfo(<int>[0]));
+        // DartEntry.ELEMENT - set in recordElementData
+        dartEntry.setValue(DartEntry.EXPORTED_LIBRARIES, Source.EMPTY_LIST);
+        dartEntry.setValue(DartEntry.IMPORTED_LIBRARIES, Source.EMPTY_LIST);
+        dartEntry.setValue(DartEntry.INCLUDED_PARTS, Source.EMPTY_LIST);
+        // DartEntry.IS_CLIENT - set in recordElementData
+        // DartEntry.IS_LAUNCHABLE - set in recordElementData
+        dartEntry.setValue(DartEntry.PARSE_ERRORS, AnalysisError.NO_ERRORS);
+        dartEntry.setState(DartEntry.PARSED_UNIT, CacheState.FLUSHED);
+        dartEntry.setState(DartEntry.PUBLIC_NAMESPACE, CacheState.FLUSHED);
+        dartEntry.setValue(DartEntry.SCAN_ERRORS, AnalysisError.NO_ERRORS);
+        dartEntry.setValue(DartEntry.SOURCE_KIND, SourceKind.LIBRARY);
+        dartEntry.setState(DartEntry.TOKEN_STREAM, CacheState.FLUSHED);
+        dartEntry.setValueInLibrary(DartEntry.RESOLUTION_ERRORS, librarySource,
+            AnalysisError.NO_ERRORS);
+        dartEntry.setStateInLibrary(
+            DartEntry.RESOLVED_UNIT, librarySource, CacheState.FLUSHED);
+        dartEntry.setValueInLibrary(DartEntry.VERIFICATION_ERRORS,
+            librarySource, AnalysisError.NO_ERRORS);
+        dartEntry.setValueInLibrary(
+            DartEntry.HINTS, librarySource, AnalysisError.NO_ERRORS);
+        dartEntry.setValueInLibrary(
+            DartEntry.LINTS, librarySource, AnalysisError.NO_ERRORS);
+      }
+    });
+  }
+
+  /**
+   * Record the results produced by performing a [task] and return the cache
+   * entry associated with the results.
+   */
+  DartEntry recordResolveDartLibraryCycleTaskResults(
+      ResolveDartLibraryCycleTask task) {
+    LibraryResolver2 resolver = task.libraryResolver;
+    CaughtException thrownException = task.exception;
+    Source unitSource = task.unitSource;
+    DartEntry unitEntry = _getReadableDartEntry(unitSource);
+    if (resolver != null) {
+      //
+      // The resolver should only be null if an exception was thrown before (or
+      // while) it was being created.
+      //
+      List<ResolvableLibrary> resolvedLibraries = resolver.resolvedLibraries;
+      if (resolvedLibraries == null) {
+        //
+        // The resolved libraries should only be null if an exception was thrown
+        // during resolution.
+        //
+        if (thrownException == null) {
+          var message = "In recordResolveDartLibraryCycleTaskResults, "
+              "resolvedLibraries was null and there was no thrown exception";
+          unitEntry.recordResolutionError(
+              new CaughtException(new AnalysisException(message), null));
+        } else {
+          unitEntry.recordResolutionError(thrownException);
+        }
+        _removeFromCache(unitSource);
+        if (thrownException != null) {
+          throw new AnalysisException('<rethrow>', thrownException);
+        }
+        return unitEntry;
+      }
+      Source htmlSource = sourceFactory.forUri(DartSdk.DART_HTML);
+      RecordingErrorListener errorListener = resolver.errorListener;
+      for (ResolvableLibrary library in resolvedLibraries) {
+        Source librarySource = library.librarySource;
+        for (Source source in library.compilationUnitSources) {
+          CompilationUnit unit = library.getAST(source);
+          List<AnalysisError> errors = errorListener.getErrorsForSource(source);
+          LineInfo lineInfo = getLineInfo(source);
+          DartEntry dartEntry = _cache.get(source);
+          if (thrownException == null) {
+            dartEntry.setState(DartEntry.PARSED_UNIT, CacheState.FLUSHED);
+            dartEntry.setValueInLibrary(
+                DartEntry.RESOLVED_UNIT, librarySource, unit);
+            dartEntry.setValueInLibrary(
+                DartEntry.RESOLUTION_ERRORS, librarySource, errors);
+            if (source == librarySource) {
+              _recordElementData(
+                  dartEntry, library.libraryElement, librarySource, htmlSource);
+            }
+            _cache.storedAst(source);
+          } else {
+            dartEntry.recordResolutionErrorInLibrary(
+                librarySource, thrownException);
+          }
+          if (source != librarySource) {
+            _workManager.add(source, SourcePriority.PRIORITY_PART);
+          }
+          ChangeNoticeImpl notice = getNotice(source);
+          notice.resolvedDartUnit = unit;
+          notice.setErrors(dartEntry.allErrors, lineInfo);
+        }
+      }
+    }
+    if (thrownException != null) {
+      throw new AnalysisException('<rethrow>', thrownException);
+    }
+    return unitEntry;
+  }
+
+  /**
+   * Record the results produced by performing a [task] and return the cache
+   * entry associated with the results.
+   */
+  DartEntry recordResolveDartLibraryTaskResults(ResolveDartLibraryTask task) {
+    LibraryResolver resolver = task.libraryResolver;
+    CaughtException thrownException = task.exception;
+    Source unitSource = task.unitSource;
+    DartEntry unitEntry = _getReadableDartEntry(unitSource);
+    if (resolver != null) {
+      //
+      // The resolver should only be null if an exception was thrown before (or
+      // while) it was being created.
+      //
+      Set<Library> resolvedLibraries = resolver.resolvedLibraries;
+      if (resolvedLibraries == null) {
+        //
+        // The resolved libraries should only be null if an exception was thrown
+        // during resolution.
+        //
+        if (thrownException == null) {
+          String message = "In recordResolveDartLibraryTaskResults, "
+              "resolvedLibraries was null and there was no thrown exception";
+          unitEntry.recordResolutionError(
+              new CaughtException(new AnalysisException(message), null));
+        } else {
+          unitEntry.recordResolutionError(thrownException);
+        }
+        _removeFromCache(unitSource);
+        if (thrownException != null) {
+          throw new AnalysisException('<rethrow>', thrownException);
+        }
+        return unitEntry;
+      }
+      Source htmlSource = sourceFactory.forUri(DartSdk.DART_HTML);
+      RecordingErrorListener errorListener = resolver.errorListener;
+      for (Library library in resolvedLibraries) {
+        Source librarySource = library.librarySource;
+        for (Source source in library.compilationUnitSources) {
+          CompilationUnit unit = library.getAST(source);
+          List<AnalysisError> errors = errorListener.getErrorsForSource(source);
+          LineInfo lineInfo = getLineInfo(source);
+          DartEntry dartEntry = _cache.get(source);
+          if (thrownException == null) {
+            dartEntry.setValue(SourceEntry.LINE_INFO, lineInfo);
+            dartEntry.setState(DartEntry.PARSED_UNIT, CacheState.FLUSHED);
+            dartEntry.setValueInLibrary(
+                DartEntry.RESOLVED_UNIT, librarySource, unit);
+            dartEntry.setValueInLibrary(
+                DartEntry.RESOLUTION_ERRORS, librarySource, errors);
+            if (source == librarySource) {
+              _recordElementData(
+                  dartEntry, library.libraryElement, librarySource, htmlSource);
+            }
+            _cache.storedAst(source);
+          } else {
+            dartEntry.recordResolutionErrorInLibrary(
+                librarySource, thrownException);
+            _removeFromCache(source);
+          }
+          if (source != librarySource) {
+            _workManager.add(source, SourcePriority.PRIORITY_PART);
+          }
+          ChangeNoticeImpl notice = getNotice(source);
+          notice.resolvedDartUnit = unit;
+          notice.setErrors(dartEntry.allErrors, lineInfo);
+        }
+      }
+    }
+    if (thrownException != null) {
+      throw new AnalysisException('<rethrow>', thrownException);
+    }
+    return unitEntry;
+  }
+
+  @override
+  void removeListener(AnalysisListener listener) {
+    _listeners.remove(listener);
+  }
+
+  @override
+  CompilationUnit resolveCompilationUnit(
+      Source unitSource, LibraryElement library) {
+    if (library == null) {
+      return null;
+    }
+    return resolveCompilationUnit2(unitSource, library.source);
+  }
+
+  @override
+  CompilationUnit resolveCompilationUnit2(
+          Source unitSource, Source librarySource) =>
+      _getDartResolutionData2(
+          unitSource, librarySource, DartEntry.RESOLVED_UNIT, null);
+
+  @override
+  @deprecated
+  ht.HtmlUnit resolveHtmlUnit(Source htmlSource) {
+    computeHtmlElement(htmlSource);
+    return parseHtmlUnit(htmlSource);
+  }
+
+  @override
+  void setChangedContents(Source source, String contents, int offset,
+      int oldLength, int newLength) {
+    if (_contentRangeChanged(source, contents, offset, oldLength, newLength)) {
+      _onSourcesChangedController.add(new SourcesChangedEvent.changedRange(
+          source, contents, offset, oldLength, newLength));
+    }
+  }
+
+  @override
+  void setContents(Source source, String contents) {
+    _contentsChanged(source, contents, true);
+  }
+
+  @override
+  bool shouldErrorsBeAnalyzed(Source source, Object entry) {
+    DartEntry dartEntry = entry;
+    if (source.isInSystemLibrary) {
+      return _generateSdkErrors;
+    } else if (!dartEntry.explicitlyAdded) {
+      return _generateImplicitErrors;
+    } else {
+      return true;
+    }
+  }
+
+  @override
+  void test_flushAstStructures(Source source) {
+    DartEntry dartEntry = getReadableSourceEntryOrNull(source);
+    dartEntry.flushAstStructures();
+  }
+
+  @override
+  bool validateCacheConsistency() {
+    int consistencyCheckStart = JavaSystem.nanoTime();
+    List<Source> changedSources = new List<Source>();
+    List<Source> missingSources = new List<Source>();
+    MapIterator<Source, SourceEntry> iterator = _cache.iterator();
+    while (iterator.moveNext()) {
+      Source source = iterator.key;
+      SourceEntry sourceEntry = iterator.value;
+      int sourceTime = getModificationStamp(source);
+      if (sourceTime != sourceEntry.modificationTime) {
+        changedSources.add(source);
+      }
+      if (sourceEntry.exception != null) {
+        if (!exists(source)) {
+          missingSources.add(source);
+        }
+      }
+    }
+    int count = changedSources.length;
+    for (int i = 0; i < count; i++) {
+      _sourceChanged(changedSources[i]);
+    }
+    int removalCount = 0;
+    for (Source source in missingSources) {
+      if (getLibrariesContaining(source).isEmpty &&
+          getLibrariesDependingOn(source).isEmpty) {
+        _removeFromCache(source);
+        removalCount++;
+      }
+    }
+    int consistencyCheckEnd = JavaSystem.nanoTime();
+    if (changedSources.length > 0 || missingSources.length > 0) {
+      StringBuffer buffer = new StringBuffer();
+      buffer.write("Consistency check took ");
+      buffer.write((consistencyCheckEnd - consistencyCheckStart) / 1000000.0);
+      buffer.writeln(" ms and found");
+      buffer.write("  ");
+      buffer.write(changedSources.length);
+      buffer.writeln(" inconsistent entries");
+      buffer.write("  ");
+      buffer.write(missingSources.length);
+      buffer.write(" missing sources (");
+      buffer.write(removalCount);
+      buffer.writeln(" removed");
+      for (Source source in missingSources) {
+        buffer.write("    ");
+        buffer.writeln(source.fullName);
+      }
+      _logInformation(buffer.toString());
+    }
+    return changedSources.length > 0;
+  }
+
+  @deprecated
+  @override
+  void visitCacheItems(void callback(Source source, SourceEntry dartEntry,
+      DataDescriptor rowDesc, CacheState state)) {
+    bool hintsEnabled = _options.hint;
+    bool lintsEnabled = _options.lint;
+    MapIterator<Source, SourceEntry> iterator = _cache.iterator();
+    while (iterator.moveNext()) {
+      Source source = iterator.key;
+      SourceEntry sourceEntry = iterator.value;
+      for (DataDescriptor descriptor in sourceEntry.descriptors) {
+        if (descriptor == DartEntry.SOURCE_KIND) {
+          // The source kind is always valid, so the state isn't interesting.
+          continue;
+        } else if (descriptor == DartEntry.CONTAINING_LIBRARIES) {
+          // The list of containing libraries is always valid, so the state
+          // isn't interesting.
+          continue;
+        } else if (descriptor == DartEntry.PUBLIC_NAMESPACE) {
+          // The public namespace isn't computed by performAnalysisTask()
+          // and therefore isn't interesting.
+          continue;
+        } else if (descriptor == HtmlEntry.HINTS) {
+          // We are not currently recording any hints related to HTML.
+          continue;
+        }
+        callback(
+            source, sourceEntry, descriptor, sourceEntry.getState(descriptor));
+      }
+      if (sourceEntry is DartEntry) {
+        // get library-specific values
+        List<Source> librarySources = getLibrariesContaining(source);
+        for (Source librarySource in librarySources) {
+          for (DataDescriptor descriptor in sourceEntry.libraryDescriptors) {
+            if (descriptor == DartEntry.BUILT_ELEMENT ||
+                descriptor == DartEntry.BUILT_UNIT) {
+              // These values are not currently being computed, so their state
+              // is not interesting.
+              continue;
+            } else if (!sourceEntry.explicitlyAdded &&
+                !_generateImplicitErrors &&
+                (descriptor == DartEntry.VERIFICATION_ERRORS ||
+                    descriptor == DartEntry.HINTS ||
+                    descriptor == DartEntry.LINTS)) {
+              continue;
+            } else if (source.isInSystemLibrary &&
+                !_generateSdkErrors &&
+                (descriptor == DartEntry.VERIFICATION_ERRORS ||
+                    descriptor == DartEntry.HINTS ||
+                    descriptor == DartEntry.LINTS)) {
+              continue;
+            } else if (!hintsEnabled && descriptor == DartEntry.HINTS) {
+              continue;
+            } else if (!lintsEnabled && descriptor == DartEntry.LINTS) {
+              continue;
+            }
+            callback(librarySource, sourceEntry, descriptor,
+                sourceEntry.getStateInLibrary(descriptor, librarySource));
+          }
+        }
+      }
+    }
+  }
+
+  @override
+  void visitContentCache(ContentCacheVisitor visitor) {
+    _contentCache.accept(visitor);
+  }
+
+  /**
+   * Record that we have accessed the AST structure associated with the given
+   * [source]. At the moment, there is no differentiation between the parsed and
+   * resolved forms of the AST.
+   */
+  void _accessedAst(Source source) {
+    _cache.accessedAst(source);
+  }
+
+  /**
+   * Add all of the sources contained in the given source [container] to the
+   * given list of [sources].
+   */
+  void _addSourcesInContainer(List<Source> sources, SourceContainer container) {
+    MapIterator<Source, SourceEntry> iterator = _cache.iterator();
+    while (iterator.moveNext()) {
+      Source source = iterator.key;
+      if (container.contains(source)) {
+        sources.add(source);
+      }
+    }
+  }
+
+  /**
+   * Given the [unitSource] of a Dart file and the [librarySource] of the
+   * library that contains it, return a cache entry in which the state of the
+   * data represented by the given [descriptor] is either [CacheState.VALID] or
+   * [CacheState.ERROR]. This method assumes that the data can be produced by
+   * generating hints for the library if the data is not already cached. The
+   * [dartEntry] is the cache entry associated with the Dart file.
+   *
+   * Throws an [AnalysisException] if data could not be returned because the
+   * source could not be parsed.
+   */
+  DartEntry _cacheDartHintData(Source unitSource, Source librarySource,
+      DartEntry dartEntry, DataDescriptor descriptor) {
+    //
+    // Check to see whether we already have the information being requested.
+    //
+    CacheState state = dartEntry.getStateInLibrary(descriptor, librarySource);
+    while (state != CacheState.ERROR && state != CacheState.VALID) {
+      //
+      // If not, compute the information.
+      // Unless the modification date of the source continues to change,
+      // this loop will eventually terminate.
+      //
+      DartEntry libraryEntry = _getReadableDartEntry(librarySource);
+      libraryEntry = _cacheDartResolutionData(
+          librarySource, librarySource, libraryEntry, DartEntry.ELEMENT);
+      LibraryElement libraryElement = libraryEntry.getValue(DartEntry.ELEMENT);
+      CompilationUnitElement definingUnit =
+          libraryElement.definingCompilationUnit;
+      List<CompilationUnitElement> parts = libraryElement.parts;
+      List<TimestampedData<CompilationUnit>> units =
+          new List<TimestampedData<CompilationUnit>>(parts.length + 1);
+      units[0] = _getResolvedUnit(definingUnit, librarySource);
+      if (units[0] == null) {
+        Source source = definingUnit.source;
+        units[0] = new TimestampedData<CompilationUnit>(
+            getModificationStamp(source),
+            resolveCompilationUnit(source, libraryElement));
+      }
+      for (int i = 0; i < parts.length; i++) {
+        units[i + 1] = _getResolvedUnit(parts[i], librarySource);
+        if (units[i + 1] == null) {
+          Source source = parts[i].source;
+          units[i + 1] = new TimestampedData<CompilationUnit>(
+              getModificationStamp(source),
+              resolveCompilationUnit(source, libraryElement));
+        }
+      }
+      dartEntry = new GenerateDartHintsTask(
+              this, units, getLibraryElement(librarySource))
+          .perform(_resultRecorder) as DartEntry;
+      state = dartEntry.getStateInLibrary(descriptor, librarySource);
+    }
+    return dartEntry;
+  }
+
+  /**
+   * Given a source for a Dart file and the library that contains it, return a
+   * cache entry in which the state of the data represented by the given
+   * descriptor is either [CacheState.VALID] or [CacheState.ERROR]. This method
+   * assumes that the data can be produced by generating lints for the library
+   * if the data is not already cached.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   */
+  DartEntry _cacheDartLintData(Source unitSource, Source librarySource,
+      DartEntry dartEntry, DataDescriptor descriptor) {
+    //
+    // Check to see whether we already have the information being requested.
+    //
+    CacheState state = dartEntry.getStateInLibrary(descriptor, librarySource);
+    while (state != CacheState.ERROR && state != CacheState.VALID) {
+      //
+      // If not, compute the information.
+      // Unless the modification date of the source continues to change,
+      // this loop will eventually terminate.
+      //
+      DartEntry libraryEntry = _getReadableDartEntry(librarySource);
+      libraryEntry = _cacheDartResolutionData(
+          librarySource, librarySource, libraryEntry, DartEntry.ELEMENT);
+      LibraryElement libraryElement = libraryEntry.getValue(DartEntry.ELEMENT);
+      CompilationUnitElement definingUnit =
+          libraryElement.definingCompilationUnit;
+      List<CompilationUnitElement> parts = libraryElement.parts;
+      List<TimestampedData<CompilationUnit>> units =
+          new List<TimestampedData<CompilationUnit>>(parts.length + 1);
+      units[0] = _getResolvedUnit(definingUnit, librarySource);
+      if (units[0] == null) {
+        Source source = definingUnit.source;
+        units[0] = new TimestampedData<CompilationUnit>(
+            getModificationStamp(source),
+            resolveCompilationUnit(source, libraryElement));
+      }
+      for (int i = 0; i < parts.length; i++) {
+        units[i + 1] = _getResolvedUnit(parts[i], librarySource);
+        if (units[i + 1] == null) {
+          Source source = parts[i].source;
+          units[i + 1] = new TimestampedData<CompilationUnit>(
+              getModificationStamp(source),
+              resolveCompilationUnit(source, libraryElement));
+        }
+      }
+      //TODO(pquitslund): revisit if we need all units or whether one will do
+      dartEntry = new GenerateDartLintsTask(
+              this, units, getLibraryElement(librarySource))
+          .perform(_resultRecorder) as DartEntry;
+      state = dartEntry.getStateInLibrary(descriptor, librarySource);
+    }
+    return dartEntry;
+  }
+
+  /**
+   * Given a source for a Dart file, return a cache entry in which the state of
+   * the data represented by the given descriptor is either [CacheState.VALID]
+   * or [CacheState.ERROR]. This method assumes that the data can be produced by
+   * parsing the source if it is not already cached.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   */
+  DartEntry _cacheDartParseData(
+      Source source, DartEntry dartEntry, DataDescriptor descriptor) {
+    if (identical(descriptor, DartEntry.PARSED_UNIT)) {
+      if (dartEntry.hasResolvableCompilationUnit) {
+        return dartEntry;
+      }
+    }
+    //
+    // Check to see whether we already have the information being requested.
+    //
+    CacheState state = dartEntry.getState(descriptor);
+    while (state != CacheState.ERROR && state != CacheState.VALID) {
+      //
+      // If not, compute the information. Unless the modification date of the
+      // source continues to change, this loop will eventually terminate.
+      //
+      dartEntry = _cacheDartScanData(source, dartEntry, DartEntry.TOKEN_STREAM);
+      dartEntry = new ParseDartTask(
+              this,
+              source,
+              dartEntry.getValue(DartEntry.TOKEN_STREAM),
+              dartEntry.getValue(SourceEntry.LINE_INFO))
+          .perform(_resultRecorder) as DartEntry;
+      state = dartEntry.getState(descriptor);
+    }
+    return dartEntry;
+  }
+
+  /**
+   * Given a source for a Dart file and the library that contains it, return a
+   * cache entry in which the state of the data represented by the given
+   * descriptor is either [CacheState.VALID] or [CacheState.ERROR]. This method
+   * assumes that the data can be produced by resolving the source in the
+   * context of the library if it is not already cached.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   */
+  DartEntry _cacheDartResolutionData(Source unitSource, Source librarySource,
+      DartEntry dartEntry, DataDescriptor descriptor) {
+    //
+    // Check to see whether we already have the information being requested.
+    //
+    CacheState state = (identical(descriptor, DartEntry.ELEMENT))
+        ? dartEntry.getState(descriptor)
+        : dartEntry.getStateInLibrary(descriptor, librarySource);
+    while (state != CacheState.ERROR && state != CacheState.VALID) {
+      //
+      // If not, compute the information. Unless the modification date of the
+      // source continues to change, this loop will eventually terminate.
+      //
+      // TODO(brianwilkerson) As an optimization, if we already have the
+      // element model for the library we can use ResolveDartUnitTask to produce
+      // the resolved AST structure much faster.
+      dartEntry = new ResolveDartLibraryTask(this, unitSource, librarySource)
+          .perform(_resultRecorder) as DartEntry;
+      state = (identical(descriptor, DartEntry.ELEMENT))
+          ? dartEntry.getState(descriptor)
+          : dartEntry.getStateInLibrary(descriptor, librarySource);
+    }
+    return dartEntry;
+  }
+
+  /**
+   * Given a source for a Dart file, return a cache entry in which the state of
+   * the data represented by the given descriptor is either [CacheState.VALID]
+   * or [CacheState.ERROR]. This method assumes that the data can be produced by
+   * scanning the source if it is not already cached.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   */
+  DartEntry _cacheDartScanData(
+      Source source, DartEntry dartEntry, DataDescriptor descriptor) {
+    //
+    // Check to see whether we already have the information being requested.
+    //
+    CacheState state = dartEntry.getState(descriptor);
+    while (state != CacheState.ERROR && state != CacheState.VALID) {
+      //
+      // If not, compute the information. Unless the modification date of the
+      // source continues to change, this loop will eventually terminate.
+      //
+      try {
+        if (dartEntry.getState(SourceEntry.CONTENT) != CacheState.VALID) {
+          dartEntry = new GetContentTask(this, source).perform(_resultRecorder)
+              as DartEntry;
+        }
+        dartEntry = new ScanDartTask(
+                this, source, dartEntry.getValue(SourceEntry.CONTENT))
+            .perform(_resultRecorder) as DartEntry;
+      } on AnalysisException catch (exception) {
+        throw exception;
+      } catch (exception, stackTrace) {
+        throw new AnalysisException(
+            "Exception", new CaughtException(exception, stackTrace));
+      }
+      state = dartEntry.getState(descriptor);
+    }
+    return dartEntry;
+  }
+
+  /**
+   * Given a source for a Dart file and the library that contains it, return a
+   * cache entry in which the state of the data represented by the given
+   * descriptor is either [CacheState.VALID] or [CacheState.ERROR]. This method
+   * assumes that the data can be produced by verifying the source in the given
+   * library if the data is not already cached.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   */
+  DartEntry _cacheDartVerificationData(Source unitSource, Source librarySource,
+      DartEntry dartEntry, DataDescriptor descriptor) {
+    //
+    // Check to see whether we already have the information being requested.
+    //
+    CacheState state = dartEntry.getStateInLibrary(descriptor, librarySource);
+    while (state != CacheState.ERROR && state != CacheState.VALID) {
+      //
+      // If not, compute the information. Unless the modification date of the
+      // source continues to change, this loop will eventually terminate.
+      //
+      LibraryElement library = computeLibraryElement(librarySource);
+      CompilationUnit unit = resolveCompilationUnit(unitSource, library);
+      if (unit == null) {
+        throw new AnalysisException(
+            "Could not resolve compilation unit ${unitSource.fullName} in ${librarySource.fullName}");
+      }
+      dartEntry = new GenerateDartErrorsTask(this, unitSource, unit, library)
+          .perform(_resultRecorder) as DartEntry;
+      state = dartEntry.getStateInLibrary(descriptor, librarySource);
+    }
+    return dartEntry;
+  }
+
+  /**
+   * Given a source for an HTML file, return a cache entry in which all of the
+   * data represented by the state of the given descriptors is either
+   * [CacheState.VALID] or [CacheState.ERROR]. This method assumes that the data
+   * can be produced by parsing the source if it is not already cached.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   */
+  HtmlEntry _cacheHtmlParseData(
+      Source source, HtmlEntry htmlEntry, DataDescriptor descriptor) {
+    if (identical(descriptor, HtmlEntry.PARSED_UNIT)) {
+      ht.HtmlUnit unit = htmlEntry.anyParsedUnit;
+      if (unit != null) {
+        return htmlEntry;
+      }
+    }
+    //
+    // Check to see whether we already have the information being requested.
+    //
+    CacheState state = htmlEntry.getState(descriptor);
+    while (state != CacheState.ERROR && state != CacheState.VALID) {
+      //
+      // If not, compute the information. Unless the modification date of the
+      // source continues to change, this loop will eventually terminate.
+      //
+      try {
+        if (htmlEntry.getState(SourceEntry.CONTENT) != CacheState.VALID) {
+          htmlEntry = new GetContentTask(this, source).perform(_resultRecorder)
+              as HtmlEntry;
+        }
+        htmlEntry = new ParseHtmlTask(
+                this, source, htmlEntry.getValue(SourceEntry.CONTENT))
+            .perform(_resultRecorder) as HtmlEntry;
+      } on AnalysisException catch (exception) {
+        throw exception;
+      } catch (exception, stackTrace) {
+        throw new AnalysisException(
+            "Exception", new CaughtException(exception, stackTrace));
+      }
+      state = htmlEntry.getState(descriptor);
+    }
+    return htmlEntry;
+  }
+
+  /**
+   * Given a source for an HTML file, return a cache entry in which the state of
+   * the data represented by the given descriptor is either [CacheState.VALID]
+   * or [CacheState.ERROR]. This method assumes that the data can be produced by
+   * resolving the source if it is not already cached.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   */
+  HtmlEntry _cacheHtmlResolutionData(
+      Source source, HtmlEntry htmlEntry, DataDescriptor descriptor) {
+    //
+    // Check to see whether we already have the information being requested.
+    //
+    CacheState state = htmlEntry.getState(descriptor);
+    while (state != CacheState.ERROR && state != CacheState.VALID) {
+      //
+      // If not, compute the information. Unless the modification date of the
+      // source continues to change, this loop will eventually terminate.
+      //
+      htmlEntry = _cacheHtmlParseData(source, htmlEntry, HtmlEntry.PARSED_UNIT);
+      htmlEntry = new ResolveHtmlTask(this, source, htmlEntry.modificationTime,
+              htmlEntry.getValue(HtmlEntry.PARSED_UNIT))
+          .perform(_resultRecorder) as HtmlEntry;
+      state = htmlEntry.getState(descriptor);
+    }
+    return htmlEntry;
+  }
+
+  /**
+   * Remove the given [pendingFuture] from [_pendingFutureSources], since the
+   * client has indicated its computation is not needed anymore.
+   */
+  void _cancelFuture(PendingFuture pendingFuture) {
+    List<PendingFuture> pendingFutures =
+        _pendingFutureSources[pendingFuture.source];
+    if (pendingFutures != null) {
+      pendingFutures.remove(pendingFuture);
+      if (pendingFutures.isEmpty) {
+        _pendingFutureSources.remove(pendingFuture.source);
+      }
+    }
+  }
+
+  /**
+   * Compute the transitive closure of all libraries that depend on the given
+   * [library] by adding such libraries to the given collection of
+   * [librariesToInvalidate].
+   */
+  void _computeAllLibrariesDependingOn(
+      Source library, HashSet<Source> librariesToInvalidate) {
+    if (librariesToInvalidate.add(library)) {
+      for (Source dependentLibrary in getLibrariesDependingOn(library)) {
+        _computeAllLibrariesDependingOn(
+            dependentLibrary, librariesToInvalidate);
+      }
+    }
+  }
+
+  /**
+   * Return the priority that should be used when the source associated with
+   * the given [dartEntry] is added to the work manager.
+   */
+  SourcePriority _computePriority(DartEntry dartEntry) {
+    SourceKind kind = dartEntry.kind;
+    if (kind == SourceKind.LIBRARY) {
+      return SourcePriority.LIBRARY;
+    } else if (kind == SourceKind.PART) {
+      return SourcePriority.NORMAL_PART;
+    }
+    return SourcePriority.UNKNOWN;
+  }
+
+  /**
+   * Given the encoded form of a source ([encoding]), use the source factory to
+   * reconstitute the original source.
+   */
+  Source _computeSourceFromEncoding(String encoding) =>
+      _sourceFactory.fromEncoding(encoding);
+
+  /**
+   * Return `true` if the given list of [sources] contains the given
+   * [targetSource].
+   */
+  bool _contains(List<Source> sources, Source targetSource) {
+    for (Source source in sources) {
+      if (source == targetSource) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  /**
+   * Return `true` if the given list of [sources] contains any of the given
+   * [targetSources].
+   */
+  bool _containsAny(List<Source> sources, List<Source> targetSources) {
+    for (Source targetSource in targetSources) {
+      if (_contains(sources, targetSource)) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  /**
+   * Set the contents of the given [source] to the given [contents] and mark the
+   * source as having changed. The additional [offset], [oldLength] and
+   * [newLength] information is used by the context to determine what reanalysis
+   * is necessary. The method [setChangedContents] triggers a source changed
+   * event where as this method does not.
+   */
+  bool _contentRangeChanged(Source source, String contents, int offset,
+      int oldLength, int newLength) {
+    bool changed = false;
+    String originalContents = _contentCache.setContents(source, contents);
+    if (contents != null) {
+      if (contents != originalContents) {
+        if (_options.incremental) {
+          _incrementalAnalysisCache = IncrementalAnalysisCache.update(
+              _incrementalAnalysisCache,
+              source,
+              originalContents,
+              contents,
+              offset,
+              oldLength,
+              newLength,
+              _getReadableSourceEntry(source));
+        }
+        _sourceChanged(source);
+        changed = true;
+        SourceEntry sourceEntry = _cache.get(source);
+        if (sourceEntry != null) {
+          sourceEntry.modificationTime =
+              _contentCache.getModificationStamp(source);
+          sourceEntry.setValue(SourceEntry.CONTENT, contents);
+        }
+      }
+    } else if (originalContents != null) {
+      _incrementalAnalysisCache =
+          IncrementalAnalysisCache.clear(_incrementalAnalysisCache, source);
+      _sourceChanged(source);
+      changed = true;
+    }
+    return changed;
+  }
+
+  /**
+   * Set the contents of the given [source] to the given [contents] and mark the
+   * source as having changed. This has the effect of overriding the default
+   * contents of the source. If the contents are `null` the override is removed
+   * so that the default contents will be returned. If [notify] is true, a
+   * source changed event is triggered.
+   */
+  void _contentsChanged(Source source, String contents, bool notify) {
+    String originalContents = _contentCache.setContents(source, contents);
+    handleContentsChanged(source, originalContents, contents, notify);
+  }
+
+  /**
+   * Create a [GenerateDartErrorsTask] for the given [unitSource], marking the
+   * verification errors as being in-process. The compilation unit and the
+   * library can be the same if the compilation unit is the defining compilation
+   * unit of the library.
+   */
+  AnalysisContextImpl_TaskData _createGenerateDartErrorsTask(Source unitSource,
+      DartEntry unitEntry, Source librarySource, DartEntry libraryEntry) {
+    if (unitEntry.getStateInLibrary(DartEntry.RESOLVED_UNIT, librarySource) !=
+            CacheState.VALID ||
+        libraryEntry.getState(DartEntry.ELEMENT) != CacheState.VALID) {
+      return _createResolveDartLibraryTask(librarySource, libraryEntry);
+    }
+    CompilationUnit unit =
+        unitEntry.getValueInLibrary(DartEntry.RESOLVED_UNIT, librarySource);
+    if (unit == null) {
+      CaughtException exception = new CaughtException(
+          new AnalysisException(
+              "Entry has VALID state for RESOLVED_UNIT but null value for ${unitSource.fullName} in ${librarySource.fullName}"),
+          null);
+      AnalysisEngine.instance.logger
+          .logInformation(exception.toString(), exception);
+      unitEntry.recordResolutionError(exception);
+      return new AnalysisContextImpl_TaskData(null, false);
+    }
+    LibraryElement libraryElement = libraryEntry.getValue(DartEntry.ELEMENT);
+    return new AnalysisContextImpl_TaskData(
+        new GenerateDartErrorsTask(this, unitSource, unit, libraryElement),
+        false);
+  }
+
+  /**
+   * Create a [GenerateDartHintsTask] for the given [source], marking the hints
+   * as being in-process.
+   */
+  AnalysisContextImpl_TaskData _createGenerateDartHintsTask(Source source,
+      DartEntry dartEntry, Source librarySource, DartEntry libraryEntry) {
+    if (libraryEntry.getState(DartEntry.ELEMENT) != CacheState.VALID) {
+      return _createResolveDartLibraryTask(librarySource, libraryEntry);
+    }
+    LibraryElement libraryElement = libraryEntry.getValue(DartEntry.ELEMENT);
+    CompilationUnitElement definingUnit =
+        libraryElement.definingCompilationUnit;
+    List<CompilationUnitElement> parts = libraryElement.parts;
+    List<TimestampedData<CompilationUnit>> units =
+        new List<TimestampedData<CompilationUnit>>(parts.length + 1);
+    units[0] = _getResolvedUnit(definingUnit, librarySource);
+    if (units[0] == null) {
+      // TODO(brianwilkerson) We should return a ResolveDartUnitTask
+      // (unless there are multiple ASTs that need to be resolved).
+      return _createResolveDartLibraryTask(librarySource, libraryEntry);
+    }
+    for (int i = 0; i < parts.length; i++) {
+      units[i + 1] = _getResolvedUnit(parts[i], librarySource);
+      if (units[i + 1] == null) {
+        // TODO(brianwilkerson) We should return a ResolveDartUnitTask
+        // (unless there are multiple ASTs that need to be resolved).
+        return _createResolveDartLibraryTask(librarySource, libraryEntry);
+      }
+    }
+    return new AnalysisContextImpl_TaskData(
+        new GenerateDartHintsTask(this, units, libraryElement), false);
+  }
+
+  /**
+   * Create a [GenerateDartLintsTask] for the given [source], marking the lints
+   * as being in-process.
+   */
+  AnalysisContextImpl_TaskData _createGenerateDartLintsTask(Source source,
+      DartEntry dartEntry, Source librarySource, DartEntry libraryEntry) {
+    if (libraryEntry.getState(DartEntry.ELEMENT) != CacheState.VALID) {
+      return _createResolveDartLibraryTask(librarySource, libraryEntry);
+    }
+    LibraryElement libraryElement = libraryEntry.getValue(DartEntry.ELEMENT);
+    CompilationUnitElement definingUnit =
+        libraryElement.definingCompilationUnit;
+    List<CompilationUnitElement> parts = libraryElement.parts;
+    List<TimestampedData<CompilationUnit>> units =
+        new List<TimestampedData<CompilationUnit>>(parts.length + 1);
+    units[0] = _getResolvedUnit(definingUnit, librarySource);
+    if (units[0] == null) {
+      // TODO(brianwilkerson) We should return a ResolveDartUnitTask
+      // (unless there are multiple ASTs that need to be resolved).
+      return _createResolveDartLibraryTask(librarySource, libraryEntry);
+    }
+    for (int i = 0; i < parts.length; i++) {
+      units[i + 1] = _getResolvedUnit(parts[i], librarySource);
+      if (units[i + 1] == null) {
+        // TODO(brianwilkerson) We should return a ResolveDartUnitTask
+        // (unless there are multiple ASTs that need to be resolved).
+        return _createResolveDartLibraryTask(librarySource, libraryEntry);
+      }
+    }
+    //TODO(pquitslund): revisit if we need all units or whether one will do
+    return new AnalysisContextImpl_TaskData(
+        new GenerateDartLintsTask(this, units, libraryElement), false);
+  }
+
+  /**
+   * Create a [GetContentTask] for the given [source], marking the content as
+   * being in-process.
+   */
+  AnalysisContextImpl_TaskData _createGetContentTask(
+      Source source, SourceEntry sourceEntry) {
+    return new AnalysisContextImpl_TaskData(
+        new GetContentTask(this, source), false);
+  }
+
+  /**
+   * Create a [ParseDartTask] for the given [source].
+   */
+  AnalysisContextImpl_TaskData _createParseDartTask(
+      Source source, DartEntry dartEntry) {
+    if (dartEntry.getState(DartEntry.TOKEN_STREAM) != CacheState.VALID ||
+        dartEntry.getState(SourceEntry.LINE_INFO) != CacheState.VALID) {
+      return _createScanDartTask(source, dartEntry);
+    }
+    Token tokenStream = dartEntry.getValue(DartEntry.TOKEN_STREAM);
+    dartEntry.setState(DartEntry.TOKEN_STREAM, CacheState.FLUSHED);
+    return new AnalysisContextImpl_TaskData(
+        new ParseDartTask(this, source, tokenStream,
+            dartEntry.getValue(SourceEntry.LINE_INFO)),
+        false);
+  }
+
+  /**
+   * Create a [ParseHtmlTask] for the given [source].
+   */
+  AnalysisContextImpl_TaskData _createParseHtmlTask(
+      Source source, HtmlEntry htmlEntry) {
+    if (htmlEntry.getState(SourceEntry.CONTENT) != CacheState.VALID) {
+      return _createGetContentTask(source, htmlEntry);
+    }
+    String content = htmlEntry.getValue(SourceEntry.CONTENT);
+    htmlEntry.setState(SourceEntry.CONTENT, CacheState.FLUSHED);
+    return new AnalysisContextImpl_TaskData(
+        new ParseHtmlTask(this, source, content), false);
+  }
+
+  /**
+   * Create a [ResolveDartLibraryTask] for the given [source], marking ? as
+   * being in-process.
+   */
+  AnalysisContextImpl_TaskData _createResolveDartLibraryTask(
+      Source source, DartEntry dartEntry) {
+    try {
+      AnalysisContextImpl_CycleBuilder builder =
+          new AnalysisContextImpl_CycleBuilder(this);
+      PerformanceStatistics.cycles.makeCurrentWhile(() {
+        builder.computeCycleContaining(source);
+      });
+      AnalysisContextImpl_TaskData taskData = builder.taskData;
+      if (taskData != null) {
+        return taskData;
+      }
+      return new AnalysisContextImpl_TaskData(
+          new ResolveDartLibraryCycleTask(
+              this, source, source, builder.librariesInCycle),
+          false);
+    } on AnalysisException catch (exception, stackTrace) {
+      dartEntry
+          .recordResolutionError(new CaughtException(exception, stackTrace));
+      AnalysisEngine.instance.logger.logError(
+          "Internal error trying to create a ResolveDartLibraryTask",
+          new CaughtException(exception, stackTrace));
+    }
+    return new AnalysisContextImpl_TaskData(null, false);
+  }
+
+  /**
+   * Create a [ResolveHtmlTask] for the given [source], marking the resolved
+   * unit as being in-process.
+   */
+  AnalysisContextImpl_TaskData _createResolveHtmlTask(
+      Source source, HtmlEntry htmlEntry) {
+    if (htmlEntry.getState(HtmlEntry.PARSED_UNIT) != CacheState.VALID) {
+      return _createParseHtmlTask(source, htmlEntry);
+    }
+    return new AnalysisContextImpl_TaskData(
+        new ResolveHtmlTask(this, source, htmlEntry.modificationTime,
+            htmlEntry.getValue(HtmlEntry.PARSED_UNIT)),
+        false);
+  }
+
+  /**
+   * Create a [ScanDartTask] for the given [source], marking the scan errors as
+   * being in-process.
+   */
+  AnalysisContextImpl_TaskData _createScanDartTask(
+      Source source, DartEntry dartEntry) {
+    if (dartEntry.getState(SourceEntry.CONTENT) != CacheState.VALID) {
+      return _createGetContentTask(source, dartEntry);
+    }
+    String content = dartEntry.getValue(SourceEntry.CONTENT);
+    dartEntry.setState(SourceEntry.CONTENT, CacheState.FLUSHED);
+    return new AnalysisContextImpl_TaskData(
+        new ScanDartTask(this, source, content), false);
+  }
+
+  /**
+   * Create a source entry for the given [source]. Return the source entry that
+   * was created, or `null` if the source should not be tracked by this context.
+   */
+  SourceEntry _createSourceEntry(Source source, bool explicitlyAdded) {
+    String name = source.shortName;
+    if (AnalysisEngine.isHtmlFileName(name)) {
+      HtmlEntry htmlEntry = new HtmlEntry();
+      htmlEntry.modificationTime = getModificationStamp(source);
+      htmlEntry.explicitlyAdded = explicitlyAdded;
+      _cache.put(source, htmlEntry);
+      if (!explicitlyAdded) {
+        _implicitAnalysisEventsController
+            .add(new ImplicitAnalysisEvent(source, true));
+      }
+      return htmlEntry;
+    } else {
+      DartEntry dartEntry = new DartEntry();
+      dartEntry.modificationTime = getModificationStamp(source);
+      dartEntry.explicitlyAdded = explicitlyAdded;
+      _cache.put(source, dartEntry);
+      if (!explicitlyAdded) {
+        _implicitAnalysisEventsController
+            .add(new ImplicitAnalysisEvent(source, true));
+      }
+      return dartEntry;
+    }
+  }
+
+  /**
+   * Return a list containing all of the change notices that are waiting to be
+   * returned. If there are no notices, then return either `null` or an empty
+   * list, depending on the value of [nullIfEmpty].
+   */
+  List<ChangeNotice> _getChangeNotices(bool nullIfEmpty) {
+    if (_pendingNotices.isEmpty) {
+      if (nullIfEmpty) {
+        return null;
+      }
+      return ChangeNoticeImpl.EMPTY_LIST;
+    }
+    List<ChangeNotice> notices = new List.from(_pendingNotices.values);
+    _pendingNotices.clear();
+    return notices;
+  }
+
+  /**
+   * Given a source for a Dart file and the library that contains it, return the
+   * data represented by the given descriptor that is associated with that
+   * source. This method assumes that the data can be produced by generating
+   * hints for the library if it is not already cached.
+   *
+   * Throws an [AnalysisException] if data could not be returned because the
+   * source could not be resolved.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   */
+  Object _getDartHintData(Source unitSource, Source librarySource,
+      DartEntry dartEntry, DataDescriptor descriptor) {
+    dartEntry =
+        _cacheDartHintData(unitSource, librarySource, dartEntry, descriptor);
+    if (identical(descriptor, DartEntry.ELEMENT)) {
+      return dartEntry.getValue(descriptor);
+    }
+    return dartEntry.getValueInLibrary(descriptor, librarySource);
+  }
+
+  /**
+   * Given a source for a Dart file and the library that contains it, return the
+   * data represented by the given descriptor that is associated with that
+   * source. This method assumes that the data can be produced by generating
+   * lints for the library if it is not already cached.
+   *
+   * Throws an [AnalysisException] if data could not be returned because the
+   * source could not be resolved.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   */
+  Object _getDartLintData(Source unitSource, Source librarySource,
+      DartEntry dartEntry, DataDescriptor descriptor) {
+    dartEntry =
+        _cacheDartLintData(unitSource, librarySource, dartEntry, descriptor);
+    if (identical(descriptor, DartEntry.ELEMENT)) {
+      return dartEntry.getValue(descriptor);
+    }
+    return dartEntry.getValueInLibrary(descriptor, librarySource);
+  }
+
+  /**
+   * Given a source for a Dart file, return the data represented by the given
+   * descriptor that is associated with that source. This method assumes that
+   * the data can be produced by parsing the source if it is not already cached.
+   *
+   * Throws an [AnalysisException] if data could not be returned because the
+   * source could not be parsed.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   */
+  Object _getDartParseData(
+      Source source, DartEntry dartEntry, DataDescriptor descriptor) {
+    dartEntry = _cacheDartParseData(source, dartEntry, descriptor);
+    if (identical(descriptor, DartEntry.PARSED_UNIT)) {
+      _accessedAst(source);
+      return dartEntry.anyParsedCompilationUnit;
+    }
+    return dartEntry.getValue(descriptor);
+  }
+
+  /**
+   * Given a source for a Dart file, return the data represented by the given
+   * descriptor that is associated with that source, or the given default value
+   * if the source is not a Dart file. This method assumes that the data can be
+   * produced by parsing the source if it is not already cached.
+   *
+   * Throws an [AnalysisException] if data could not be returned because the
+   * source could not be parsed.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   */
+  Object _getDartParseData2(
+      Source source, DataDescriptor descriptor, Object defaultValue) {
+    DartEntry dartEntry = _getReadableDartEntry(source);
+    if (dartEntry == null) {
+      return defaultValue;
+    }
+    try {
+      return _getDartParseData(source, dartEntry, descriptor);
+    } on ObsoleteSourceAnalysisException catch (exception, stackTrace) {
+      AnalysisEngine.instance.logger.logInformation(
+          "Could not compute $descriptor",
+          new CaughtException(exception, stackTrace));
+      return defaultValue;
+    }
+  }
+
+  /**
+   * Given a source for a Dart file and the library that contains it, return the
+   * data represented by the given descriptor that is associated with that
+   * source. This method assumes that the data can be produced by resolving the
+   * source in the context of the library if it is not already cached.
+   *
+   * Throws an [AnalysisException] if data could not be returned because the
+   * source could not be resolved.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   */
+  Object _getDartResolutionData(Source unitSource, Source librarySource,
+      DartEntry dartEntry, DataDescriptor descriptor) {
+    dartEntry = _cacheDartResolutionData(
+        unitSource, librarySource, dartEntry, descriptor);
+    if (identical(descriptor, DartEntry.ELEMENT)) {
+      return dartEntry.getValue(descriptor);
+    } else if (identical(descriptor, DartEntry.RESOLVED_UNIT)) {
+      _accessedAst(unitSource);
+    }
+    return dartEntry.getValueInLibrary(descriptor, librarySource);
+  }
+
+  /**
+   * Given a source for a Dart file and the library that contains it, return the
+   * data represented by the given descriptor that is associated with that
+   * source, or the given default value if the source is not a Dart file. This
+   * method assumes that the data can be produced by resolving the source in the
+   * context of the library if it is not already cached.
+   *
+   * Throws an [AnalysisException] if data could not be returned because the
+   * source could not be resolved.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   */
+  Object _getDartResolutionData2(Source unitSource, Source librarySource,
+      DataDescriptor descriptor, Object defaultValue) {
+    DartEntry dartEntry = _getReadableDartEntry(unitSource);
+    if (dartEntry == null) {
+      return defaultValue;
+    }
+    try {
+      return _getDartResolutionData(
+          unitSource, librarySource, dartEntry, descriptor);
+    } on ObsoleteSourceAnalysisException catch (exception, stackTrace) {
+      AnalysisEngine.instance.logger.logInformation(
+          "Could not compute $descriptor",
+          new CaughtException(exception, stackTrace));
+      return defaultValue;
+    }
+  }
+
+  /**
+   * Given a source for a Dart file, return the data represented by the given
+   * descriptor that is associated with that source. This method assumes that
+   * the data can be produced by scanning the source if it is not already
+   * cached.
+   *
+   * Throws an [AnalysisException] if data could not be returned because the
+   * source could not be scanned.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   */
+  Object _getDartScanData(
+      Source source, DartEntry dartEntry, DataDescriptor descriptor) {
+    dartEntry = _cacheDartScanData(source, dartEntry, descriptor);
+    return dartEntry.getValue(descriptor);
+  }
+
+  /**
+   * Given a source for a Dart file, return the data represented by the given
+   * descriptor that is associated with that source, or the given default value
+   * if the source is not a Dart file. This method assumes that the data can be
+   * produced by scanning the source if it is not already cached.
+   *
+   * Throws an [AnalysisException] if data could not be returned because the
+   * source could not be scanned.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   */
+  Object _getDartScanData2(
+      Source source, DataDescriptor descriptor, Object defaultValue) {
+    DartEntry dartEntry = _getReadableDartEntry(source);
+    if (dartEntry == null) {
+      return defaultValue;
+    }
+    try {
+      return _getDartScanData(source, dartEntry, descriptor);
+    } on ObsoleteSourceAnalysisException catch (exception, stackTrace) {
+      AnalysisEngine.instance.logger.logInformation(
+          "Could not compute $descriptor",
+          new CaughtException(exception, stackTrace));
+      return defaultValue;
+    }
+  }
+
+  /**
+   * Given a source for a Dart file and the library that contains it, return the
+   * data represented by the given descriptor that is associated with that
+   * source. This method assumes that the data can be produced by verifying the
+   * source within the given library if it is not already cached.
+   *
+   * Throws an [AnalysisException] if data could not be returned because the
+   * source could not be resolved.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   */
+  Object _getDartVerificationData(Source unitSource, Source librarySource,
+      DartEntry dartEntry, DataDescriptor descriptor) {
+    dartEntry = _cacheDartVerificationData(
+        unitSource, librarySource, dartEntry, descriptor);
+    return dartEntry.getValueInLibrary(descriptor, librarySource);
+  }
+
+  /**
+   * Given a source for an HTML file, return the data represented by the given
+   * descriptor that is associated with that source, or the given default value
+   * if the source is not an HTML file. This method assumes that the data can be
+   * produced by parsing the source if it is not already cached.
+   *
+   * Throws an [AnalysisException] if data could not be returned because the
+   * source could not be parsed.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   */
+  Object _getHtmlParseData(
+      Source source, DataDescriptor descriptor, Object defaultValue) {
+    HtmlEntry htmlEntry = _getReadableHtmlEntry(source);
+    if (htmlEntry == null) {
+      return defaultValue;
+    }
+    htmlEntry = _cacheHtmlParseData(source, htmlEntry, descriptor);
+    if (identical(descriptor, HtmlEntry.PARSED_UNIT)) {
+      _accessedAst(source);
+      return htmlEntry.anyParsedUnit;
+    }
+    return htmlEntry.getValue(descriptor);
+  }
+
+  /**
+   * Given a source for an HTML file, return the data represented by the given
+   * descriptor that is associated with that source, or the given default value
+   * if the source is not an HTML file. This method assumes that the data can be
+   * produced by resolving the source if it is not already cached.
+   *
+   * Throws an [AnalysisException] if data could not be returned because the
+   * source could not be resolved.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   */
+  Object _getHtmlResolutionData(
+      Source source, DataDescriptor descriptor, Object defaultValue) {
+    HtmlEntry htmlEntry = _getReadableHtmlEntry(source);
+    if (htmlEntry == null) {
+      return defaultValue;
+    }
+    try {
+      return _getHtmlResolutionData2(source, htmlEntry, descriptor);
+    } on ObsoleteSourceAnalysisException catch (exception, stackTrace) {
+      AnalysisEngine.instance.logger.logInformation(
+          "Could not compute $descriptor",
+          new CaughtException(exception, stackTrace));
+      return defaultValue;
+    }
+  }
+
+  /**
+   * Given a source for an HTML file, return the data represented by the given
+   * descriptor that is associated with that source. This method assumes that
+   * the data can be produced by resolving the source if it is not already
+   * cached.
+   *
+   * Throws an [AnalysisException] if data could not be returned because the
+   * source could not be resolved.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment.
+   */
+  Object _getHtmlResolutionData2(
+      Source source, HtmlEntry htmlEntry, DataDescriptor descriptor) {
+    htmlEntry = _cacheHtmlResolutionData(source, htmlEntry, descriptor);
+    if (identical(descriptor, HtmlEntry.RESOLVED_UNIT)) {
+      _accessedAst(source);
+    }
+    return htmlEntry.getValue(descriptor);
+  }
+
+  /**
+   * Look at the given [source] to see whether a task needs to be performed
+   * related to it. Return the task that should be performed, or `null` if there
+   * is no more work to be done for the source.
+   */
+  AnalysisContextImpl_TaskData _getNextAnalysisTaskForSource(
+      Source source,
+      SourceEntry sourceEntry,
+      bool isPriority,
+      bool hintsEnabled,
+      bool lintsEnabled) {
+    // Refuse to generate tasks for html based files that are above 1500 KB
+    if (_isTooBigHtmlSourceEntry(source, sourceEntry)) {
+      // TODO (jwren) we still need to report an error of some kind back to the
+      // client.
+      return new AnalysisContextImpl_TaskData(null, false);
+    }
+    if (sourceEntry == null) {
+      return new AnalysisContextImpl_TaskData(null, false);
+    }
+    CacheState contentState = sourceEntry.getState(SourceEntry.CONTENT);
+    if (contentState == CacheState.INVALID) {
+      return _createGetContentTask(source, sourceEntry);
+    } else if (contentState == CacheState.IN_PROCESS) {
+      // We are already in the process of getting the content.
+      // There's nothing else we can do with this source until that's complete.
+      return new AnalysisContextImpl_TaskData(null, true);
+    } else if (contentState == CacheState.ERROR) {
+      // We have done all of the analysis we can for this source because we
+      // cannot get its content.
+      return new AnalysisContextImpl_TaskData(null, false);
+    }
+    if (sourceEntry is DartEntry) {
+      DartEntry dartEntry = sourceEntry;
+      CacheState scanErrorsState = dartEntry.getState(DartEntry.SCAN_ERRORS);
+      if (scanErrorsState == CacheState.INVALID ||
+          (isPriority && scanErrorsState == CacheState.FLUSHED)) {
+        return _createScanDartTask(source, dartEntry);
+      }
+      CacheState parseErrorsState = dartEntry.getState(DartEntry.PARSE_ERRORS);
+      if (parseErrorsState == CacheState.INVALID ||
+          (isPriority && parseErrorsState == CacheState.FLUSHED)) {
+        return _createParseDartTask(source, dartEntry);
+      }
+      if (isPriority && parseErrorsState != CacheState.ERROR) {
+        if (!dartEntry.hasResolvableCompilationUnit) {
+          return _createParseDartTask(source, dartEntry);
+        }
+      }
+      SourceKind kind = dartEntry.getValue(DartEntry.SOURCE_KIND);
+      if (kind == SourceKind.UNKNOWN) {
+        return _createParseDartTask(source, dartEntry);
+      } else if (kind == SourceKind.LIBRARY) {
+        CacheState elementState = dartEntry.getState(DartEntry.ELEMENT);
+        if (elementState == CacheState.INVALID) {
+          return _createResolveDartLibraryTask(source, dartEntry);
+        }
+      }
+      List<Source> librariesContaining = dartEntry.containingLibraries;
+      for (Source librarySource in librariesContaining) {
+        SourceEntry librarySourceEntry = _cache.get(librarySource);
+        if (librarySourceEntry is DartEntry) {
+          DartEntry libraryEntry = librarySourceEntry;
+          CacheState elementState = libraryEntry.getState(DartEntry.ELEMENT);
+          if (elementState == CacheState.INVALID ||
+              (isPriority && elementState == CacheState.FLUSHED)) {
+//            return createResolveDartLibraryTask(librarySource, (DartEntry) libraryEntry);
+            return new AnalysisContextImpl_TaskData(
+                new ResolveDartLibraryTask(this, source, librarySource), false);
+          }
+          CacheState resolvedUnitState = dartEntry.getStateInLibrary(
+              DartEntry.RESOLVED_UNIT, librarySource);
+          if (resolvedUnitState == CacheState.INVALID ||
+              (isPriority && resolvedUnitState == CacheState.FLUSHED)) {
+            //
+            // The commented out lines below are an optimization that doesn't
+            // quite work yet. The problem is that if the source was not
+            // resolved because it wasn't part of any library, then there won't
+            // be any elements in the element model that we can use to resolve
+            // it.
+            //
+//            LibraryElement libraryElement = libraryEntry.getValue(DartEntry.ELEMENT);
+//            if (libraryElement != null) {
+//              return new ResolveDartUnitTask(this, source, libraryElement);
+//            }
+            // Possibly replace with:
+//             return createResolveDartLibraryTask(librarySource, (DartEntry) libraryEntry);
+            return new AnalysisContextImpl_TaskData(
+                new ResolveDartLibraryTask(this, source, librarySource), false);
+          }
+          if (shouldErrorsBeAnalyzed(source, dartEntry)) {
+            CacheState verificationErrorsState = dartEntry.getStateInLibrary(
+                DartEntry.VERIFICATION_ERRORS, librarySource);
+            if (verificationErrorsState == CacheState.INVALID ||
+                (isPriority && verificationErrorsState == CacheState.FLUSHED)) {
+              return _createGenerateDartErrorsTask(
+                  source, dartEntry, librarySource, libraryEntry);
+            }
+            if (hintsEnabled) {
+              CacheState hintsState =
+                  dartEntry.getStateInLibrary(DartEntry.HINTS, librarySource);
+              if (hintsState == CacheState.INVALID ||
+                  (isPriority && hintsState == CacheState.FLUSHED)) {
+                return _createGenerateDartHintsTask(
+                    source, dartEntry, librarySource, libraryEntry);
+              }
+            }
+            if (lintsEnabled) {
+              CacheState lintsState =
+                  dartEntry.getStateInLibrary(DartEntry.LINTS, librarySource);
+              if (lintsState == CacheState.INVALID ||
+                  (isPriority && lintsState == CacheState.FLUSHED)) {
+                return _createGenerateDartLintsTask(
+                    source, dartEntry, librarySource, libraryEntry);
+              }
+            }
+          }
+        }
+      }
+    } else if (sourceEntry is HtmlEntry) {
+      HtmlEntry htmlEntry = sourceEntry;
+      CacheState parseErrorsState = htmlEntry.getState(HtmlEntry.PARSE_ERRORS);
+      if (parseErrorsState == CacheState.INVALID ||
+          (isPriority && parseErrorsState == CacheState.FLUSHED)) {
+        return _createParseHtmlTask(source, htmlEntry);
+      }
+      if (isPriority && parseErrorsState != CacheState.ERROR) {
+        ht.HtmlUnit parsedUnit = htmlEntry.anyParsedUnit;
+        if (parsedUnit == null) {
+          return _createParseHtmlTask(source, htmlEntry);
+        }
+      }
+      CacheState resolvedUnitState =
+          htmlEntry.getState(HtmlEntry.RESOLVED_UNIT);
+      if (resolvedUnitState == CacheState.INVALID ||
+          (isPriority && resolvedUnitState == CacheState.FLUSHED)) {
+        return _createResolveHtmlTask(source, htmlEntry);
+      }
+    }
+    return new AnalysisContextImpl_TaskData(null, false);
+  }
+
+  /**
+   * Return the cache entry associated with the given [source], or `null` if the
+   * source is not a Dart file.
+   *
+   * @param source the source for which a cache entry is being sought
+   * @return the source cache entry associated with the given source
+   */
+  DartEntry _getReadableDartEntry(Source source) {
+    SourceEntry sourceEntry = _cache.get(source);
+    if (sourceEntry == null) {
+      sourceEntry = _createSourceEntry(source, false);
+    }
+    if (sourceEntry is DartEntry) {
+      return sourceEntry;
+    }
+    return null;
+  }
+
+  /**
+   * Return the cache entry associated with the given [source], or `null` if the
+   * source is not an HTML file.
+   */
+  HtmlEntry _getReadableHtmlEntry(Source source) {
+    SourceEntry sourceEntry = _cache.get(source);
+    if (sourceEntry == null) {
+      sourceEntry = _createSourceEntry(source, false);
+    }
+    if (sourceEntry is HtmlEntry) {
+      return sourceEntry;
+    }
+    return null;
+  }
+
+  /**
+   * Return the cache entry associated with the given [source], creating it if
+   * necessary.
+   */
+  SourceEntry _getReadableSourceEntry(Source source) {
+    SourceEntry sourceEntry = _cache.get(source);
+    if (sourceEntry == null) {
+      sourceEntry = _createSourceEntry(source, false);
+    }
+    return sourceEntry;
+  }
+
+  /**
+   * Return a resolved compilation unit corresponding to the given [element] in
+   * the library defined by the given [librarySource], or `null` if the
+   * information is not cached.
+   */
+  TimestampedData<CompilationUnit> _getResolvedUnit(
+      CompilationUnitElement element, Source librarySource) {
+    SourceEntry sourceEntry = _cache.get(element.source);
+    if (sourceEntry is DartEntry) {
+      DartEntry dartEntry = sourceEntry;
+      if (dartEntry.getStateInLibrary(DartEntry.RESOLVED_UNIT, librarySource) ==
+          CacheState.VALID) {
+        return new TimestampedData<CompilationUnit>(
+            dartEntry.modificationTime,
+            dartEntry.getValueInLibrary(
+                DartEntry.RESOLVED_UNIT, librarySource));
+      }
+    }
+    return null;
+  }
+
+  /**
+   * Return a list containing all of the sources known to this context that have
+   * the given [kind].
+   */
+  List<Source> _getSources(SourceKind kind) {
+    List<Source> sources = new List<Source>();
+    MapIterator<Source, SourceEntry> iterator = _cache.iterator();
+    while (iterator.moveNext()) {
+      if (iterator.value.kind == kind) {
+        sources.add(iterator.key);
+      }
+    }
+    return sources;
+  }
+
+  /**
+   * Look at the given [source] to see whether a task needs to be performed
+   * related to it. If so, add the source to the set of sources that need to be
+   * processed. This method duplicates, and must therefore be kept in sync with,
+   * [_getNextAnalysisTaskForSource]. This method is intended to be used for
+   * testing purposes only.
+   */
+  void _getSourcesNeedingProcessing(
+      Source source,
+      SourceEntry sourceEntry,
+      bool isPriority,
+      bool hintsEnabled,
+      bool lintsEnabled,
+      HashSet<Source> sources) {
+    if (sourceEntry is DartEntry) {
+      DartEntry dartEntry = sourceEntry;
+      CacheState scanErrorsState = dartEntry.getState(DartEntry.SCAN_ERRORS);
+      if (scanErrorsState == CacheState.INVALID ||
+          (isPriority && scanErrorsState == CacheState.FLUSHED)) {
+        sources.add(source);
+        return;
+      }
+      CacheState parseErrorsState = dartEntry.getState(DartEntry.PARSE_ERRORS);
+      if (parseErrorsState == CacheState.INVALID ||
+          (isPriority && parseErrorsState == CacheState.FLUSHED)) {
+        sources.add(source);
+        return;
+      }
+      if (isPriority) {
+        if (!dartEntry.hasResolvableCompilationUnit) {
+          sources.add(source);
+          return;
+        }
+      }
+      for (Source librarySource in getLibrariesContaining(source)) {
+        SourceEntry libraryEntry = _cache.get(librarySource);
+        if (libraryEntry is DartEntry) {
+          CacheState elementState = libraryEntry.getState(DartEntry.ELEMENT);
+          if (elementState == CacheState.INVALID ||
+              (isPriority && elementState == CacheState.FLUSHED)) {
+            sources.add(source);
+            return;
+          }
+          CacheState resolvedUnitState = dartEntry.getStateInLibrary(
+              DartEntry.RESOLVED_UNIT, librarySource);
+          if (resolvedUnitState == CacheState.INVALID ||
+              (isPriority && resolvedUnitState == CacheState.FLUSHED)) {
+            LibraryElement libraryElement =
+                libraryEntry.getValue(DartEntry.ELEMENT);
+            if (libraryElement != null) {
+              sources.add(source);
+              return;
+            }
+          }
+          if (shouldErrorsBeAnalyzed(source, dartEntry)) {
+            CacheState verificationErrorsState = dartEntry.getStateInLibrary(
+                DartEntry.VERIFICATION_ERRORS, librarySource);
+            if (verificationErrorsState == CacheState.INVALID ||
+                (isPriority && verificationErrorsState == CacheState.FLUSHED)) {
+              LibraryElement libraryElement =
+                  libraryEntry.getValue(DartEntry.ELEMENT);
+              if (libraryElement != null) {
+                sources.add(source);
+                return;
+              }
+            }
+            if (hintsEnabled) {
+              CacheState hintsState =
+                  dartEntry.getStateInLibrary(DartEntry.HINTS, librarySource);
+              if (hintsState == CacheState.INVALID ||
+                  (isPriority && hintsState == CacheState.FLUSHED)) {
+                LibraryElement libraryElement =
+                    libraryEntry.getValue(DartEntry.ELEMENT);
+                if (libraryElement != null) {
+                  sources.add(source);
+                  return;
+                }
+              }
+            }
+            if (lintsEnabled) {
+              CacheState lintsState =
+                  dartEntry.getStateInLibrary(DartEntry.LINTS, librarySource);
+              if (lintsState == CacheState.INVALID ||
+                  (isPriority && lintsState == CacheState.FLUSHED)) {
+                LibraryElement libraryElement =
+                    libraryEntry.getValue(DartEntry.ELEMENT);
+                if (libraryElement != null) {
+                  sources.add(source);
+                  return;
+                }
+              }
+            }
+          }
+        }
+      }
+    } else if (sourceEntry is HtmlEntry) {
+      HtmlEntry htmlEntry = sourceEntry;
+      CacheState parsedUnitState = htmlEntry.getState(HtmlEntry.PARSED_UNIT);
+      if (parsedUnitState == CacheState.INVALID ||
+          (isPriority && parsedUnitState == CacheState.FLUSHED)) {
+        sources.add(source);
+        return;
+      }
+      CacheState resolvedUnitState =
+          htmlEntry.getState(HtmlEntry.RESOLVED_UNIT);
+      if (resolvedUnitState == CacheState.INVALID ||
+          (isPriority && resolvedUnitState == CacheState.FLUSHED)) {
+        sources.add(source);
+        return;
+      }
+    }
+  }
+
+  /**
+   * Invalidate all of the resolution results computed by this context. The flag
+   * [invalidateUris] should be `true` if the cached results of converting URIs
+   * to source files should also be invalidated.
+   */
+  void _invalidateAllLocalResolutionInformation(bool invalidateUris) {
+    HashMap<Source, List<Source>> oldPartMap =
+        new HashMap<Source, List<Source>>();
+    MapIterator<Source, SourceEntry> iterator = _privatePartition.iterator();
+    while (iterator.moveNext()) {
+      Source source = iterator.key;
+      SourceEntry sourceEntry = iterator.value;
+      if (sourceEntry is HtmlEntry) {
+        HtmlEntry htmlEntry = sourceEntry;
+        htmlEntry.invalidateAllResolutionInformation(invalidateUris);
+        iterator.value = htmlEntry;
+        _workManager.add(source, SourcePriority.HTML);
+      } else if (sourceEntry is DartEntry) {
+        DartEntry dartEntry = sourceEntry;
+        oldPartMap[source] = dartEntry.getValue(DartEntry.INCLUDED_PARTS);
+        dartEntry.invalidateAllResolutionInformation(invalidateUris);
+        iterator.value = dartEntry;
+        _workManager.add(source, _computePriority(dartEntry));
+      }
+    }
+    _removeFromPartsUsingMap(oldPartMap);
+  }
+
+  /**
+   * In response to a change to at least one of the compilation units in the
+   * library defined by the given [librarySource], invalidate any results that
+   * are dependent on the result of resolving that library.
+   *
+   * <b>Note:</b> Any cache entries that were accessed before this method was
+   * invoked must be re-accessed after this method returns.
+   */
+  void _invalidateLibraryResolution(Source librarySource) {
+    // TODO(brianwilkerson) This could be optimized. There's no need to flush
+    // all of these entries if the public namespace hasn't changed, which will
+    // be a fairly common case. The question is whether we can afford the time
+    // to compute the namespace to look for differences.
+    DartEntry libraryEntry = _getReadableDartEntry(librarySource);
+    if (libraryEntry != null) {
+      List<Source> includedParts =
+          libraryEntry.getValue(DartEntry.INCLUDED_PARTS);
+      libraryEntry.invalidateAllResolutionInformation(false);
+      _workManager.add(librarySource, SourcePriority.LIBRARY);
+      for (Source partSource in includedParts) {
+        SourceEntry partEntry = _cache.get(partSource);
+        if (partEntry is DartEntry) {
+          partEntry.invalidateAllResolutionInformation(false);
+        }
+      }
+    }
+  }
+
+  /**
+   * Return `true` if the given [library] is, or depends on, 'dart:html'. The
+   * [visitedLibraries] is a collection of the libraries that have been visited,
+   * used to prevent infinite recursion.
+   */
+  bool _isClient(LibraryElement library, Source htmlSource,
+      HashSet<LibraryElement> visitedLibraries) {
+    if (visitedLibraries.contains(library)) {
+      return false;
+    }
+    if (library.source == htmlSource) {
+      return true;
+    }
+    visitedLibraries.add(library);
+    for (LibraryElement imported in library.importedLibraries) {
+      if (_isClient(imported, htmlSource, visitedLibraries)) {
+        return true;
+      }
+    }
+    for (LibraryElement exported in library.exportedLibraries) {
+      if (_isClient(exported, htmlSource, visitedLibraries)) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  bool _isTooBigHtmlSourceEntry(Source source, SourceEntry sourceEntry) =>
+      false;
+
+//  /**
+//   * Notify all of the analysis listeners that the given source is no longer included in the set of
+//   * sources that are being analyzed.
+//   *
+//   * @param source the source that is no longer being analyzed
+//   */
+//  void _notifyExcludedSource(Source source) {
+//    int count = _listeners.length;
+//    for (int i = 0; i < count; i++) {
+//      _listeners[i].excludedSource(this, source);
+//    }
+//  }
+
+//  /**
+//   * Notify all of the analysis listeners that the given source is now included in the set of
+//   * sources that are being analyzed.
+//   *
+//   * @param source the source that is now being analyzed
+//   */
+//  void _notifyIncludedSource(Source source) {
+//    int count = _listeners.length;
+//    for (int i = 0; i < count; i++) {
+//      _listeners[i].includedSource(this, source);
+//    }
+//  }
+
+//  /**
+//   * Notify all of the analysis listeners that the given Dart source was parsed.
+//   *
+//   * @param source the source that was parsed
+//   * @param unit the result of parsing the source
+//   */
+//  void _notifyParsedDart(Source source, CompilationUnit unit) {
+//    int count = _listeners.length;
+//    for (int i = 0; i < count; i++) {
+//      _listeners[i].parsedDart(this, source, unit);
+//    }
+//  }
+
+//  /**
+//   * Notify all of the analysis listeners that the given HTML source was parsed.
+//   *
+//   * @param source the source that was parsed
+//   * @param unit the result of parsing the source
+//   */
+//  void _notifyParsedHtml(Source source, ht.HtmlUnit unit) {
+//    int count = _listeners.length;
+//    for (int i = 0; i < count; i++) {
+//      _listeners[i].parsedHtml(this, source, unit);
+//    }
+//  }
+
+//  /**
+//   * Notify all of the analysis listeners that the given Dart source was resolved.
+//   *
+//   * @param source the source that was resolved
+//   * @param unit the result of resolving the source
+//   */
+//  void _notifyResolvedDart(Source source, CompilationUnit unit) {
+//    int count = _listeners.length;
+//    for (int i = 0; i < count; i++) {
+//      _listeners[i].resolvedDart(this, source, unit);
+//    }
+//  }
+
+//  /**
+//   * Notify all of the analysis listeners that the given HTML source was resolved.
+//   *
+//   * @param source the source that was resolved
+//   * @param unit the result of resolving the source
+//   */
+//  void _notifyResolvedHtml(Source source, ht.HtmlUnit unit) {
+//    int count = _listeners.length;
+//    for (int i = 0; i < count; i++) {
+//      _listeners[i].resolvedHtml(this, source, unit);
+//    }
+//  }
+
+  /**
+   * Log the given debugging [message].
+   */
+  void _logInformation(String message) {
+    AnalysisEngine.instance.logger.logInformation(message);
+  }
+
+  /**
+   * Notify all of the analysis listeners that a task is about to be performed.
+   */
+  void _notifyAboutToPerformTask(String taskDescription) {
+    int count = _listeners.length;
+    for (int i = 0; i < count; i++) {
+      _listeners[i].aboutToPerformTask(this, taskDescription);
+    }
+  }
+
+  /**
+   * Notify all of the analysis listeners that the errors associated with the
+   * given [source] has been updated to the given [errors].
+   */
+  void _notifyErrors(
+      Source source, List<AnalysisError> errors, LineInfo lineInfo) {
+    int count = _listeners.length;
+    for (int i = 0; i < count; i++) {
+      _listeners[i].computedErrors(this, source, errors, lineInfo);
+    }
+  }
+
+  /**
+   * Given that the given [source] (with the corresponding [sourceEntry]) has
+   * been invalidated, invalidate all of the libraries that depend on it.
+   */
+  void _propagateInvalidation(Source source, SourceEntry sourceEntry) {
+    if (sourceEntry is HtmlEntry) {
+      HtmlEntry htmlEntry = sourceEntry;
+      htmlEntry.modificationTime = getModificationStamp(source);
+      htmlEntry.invalidateAllInformation();
+      _cache.removedAst(source);
+      _workManager.add(source, SourcePriority.HTML);
+    } else if (sourceEntry is DartEntry) {
+      List<Source> containingLibraries = getLibrariesContaining(source);
+      List<Source> dependentLibraries = getLibrariesDependingOn(source);
+      HashSet<Source> librariesToInvalidate = new HashSet<Source>();
+      for (Source containingLibrary in containingLibraries) {
+        _computeAllLibrariesDependingOn(
+            containingLibrary, librariesToInvalidate);
+      }
+      for (Source dependentLibrary in dependentLibraries) {
+        _computeAllLibrariesDependingOn(
+            dependentLibrary, librariesToInvalidate);
+      }
+      for (Source library in librariesToInvalidate) {
+        _invalidateLibraryResolution(library);
+      }
+      DartEntry dartEntry = _cache.get(source);
+      _removeFromParts(source, dartEntry);
+      dartEntry.modificationTime = getModificationStamp(source);
+      dartEntry.invalidateAllInformation();
+      _cache.removedAst(source);
+      _workManager.add(source, SourcePriority.UNKNOWN);
+    }
+    // reset unit in the notification, it is out of date now
+    ChangeNoticeImpl notice = _pendingNotices[source];
+    if (notice != null) {
+      notice.resolvedDartUnit = null;
+      notice.resolvedHtmlUnit = null;
+    }
+  }
+
+  /**
+   * Given a [dartEntry] and a [library] element, record the library element and
+   * other information gleaned from the element in the cache entry.
+   */
+  void _recordElementData(DartEntry dartEntry, LibraryElement library,
+      Source librarySource, Source htmlSource) {
+    dartEntry.setValue(DartEntry.ELEMENT, library);
+    dartEntry.setValue(DartEntry.IS_LAUNCHABLE, library.entryPoint != null);
+    dartEntry.setValue(DartEntry.IS_CLIENT,
+        _isClient(library, htmlSource, new HashSet<LibraryElement>()));
+  }
+
+  /**
+   * Record the results produced by performing a [task] and return the cache
+   * entry associated with the results.
+   */
+  DartEntry _recordGenerateDartErrorsTask(GenerateDartErrorsTask task) {
+    Source source = task.source;
+    DartEntry dartEntry = _cache.get(source);
+    Source librarySource = task.libraryElement.source;
+    CaughtException thrownException = task.exception;
+    if (thrownException != null) {
+      dartEntry.recordVerificationErrorInLibrary(
+          librarySource, thrownException);
+      throw new AnalysisException('<rethrow>', thrownException);
+    }
+    dartEntry.setValueInLibrary(
+        DartEntry.VERIFICATION_ERRORS, librarySource, task.errors);
+    ChangeNoticeImpl notice = getNotice(source);
+    LineInfo lineInfo = dartEntry.getValue(SourceEntry.LINE_INFO);
+    notice.setErrors(dartEntry.allErrors, lineInfo);
+    return dartEntry;
+  }
+
+  /**
+   * Record the results produced by performing a [task] and return the cache
+   * entry associated with the results.
+   */
+  DartEntry _recordGenerateDartHintsTask(GenerateDartHintsTask task) {
+    Source librarySource = task.libraryElement.source;
+    CaughtException thrownException = task.exception;
+    DartEntry libraryEntry = null;
+    HashMap<Source, List<AnalysisError>> hintMap = task.hintMap;
+    if (hintMap == null) {
+      // We don't have any information about which sources to mark as invalid
+      // other than the library source.
+      DartEntry libraryEntry = _cache.get(librarySource);
+      if (thrownException == null) {
+        String message = "GenerateDartHintsTask returned a null hint map "
+            "without throwing an exception: ${librarySource.fullName}";
+        thrownException =
+            new CaughtException(new AnalysisException(message), null);
+      }
+      libraryEntry.recordHintErrorInLibrary(librarySource, thrownException);
+      throw new AnalysisException('<rethrow>', thrownException);
+    }
+    hintMap.forEach((Source unitSource, List<AnalysisError> hints) {
+      DartEntry dartEntry = _cache.get(unitSource);
+      if (unitSource == librarySource) {
+        libraryEntry = dartEntry;
+      }
+      if (thrownException == null) {
+        dartEntry.setValueInLibrary(DartEntry.HINTS, librarySource, hints);
+        ChangeNoticeImpl notice = getNotice(unitSource);
+        LineInfo lineInfo = dartEntry.getValue(SourceEntry.LINE_INFO);
+        notice.setErrors(dartEntry.allErrors, lineInfo);
+      } else {
+        dartEntry.recordHintErrorInLibrary(librarySource, thrownException);
+      }
+    });
+    if (thrownException != null) {
+      throw new AnalysisException('<rethrow>', thrownException);
+    }
+    return libraryEntry;
+  }
+
+  /**
+   * Record the results produced by performing a [task] and return the cache
+   * entry associated with the results.
+   */
+  DartEntry _recordGenerateDartLintsTask(GenerateDartLintsTask task) {
+    Source librarySource = task.libraryElement.source;
+    CaughtException thrownException = task.exception;
+    DartEntry libraryEntry = null;
+    HashMap<Source, List<AnalysisError>> lintMap = task.lintMap;
+    if (lintMap == null) {
+      // We don't have any information about which sources to mark as invalid
+      // other than the library source.
+      DartEntry libraryEntry = _cache.get(librarySource);
+      if (thrownException == null) {
+        String message = "GenerateDartLintsTask returned a null lint map "
+            "without throwing an exception: ${librarySource.fullName}";
+        thrownException =
+            new CaughtException(new AnalysisException(message), null);
+      }
+      libraryEntry.recordLintErrorInLibrary(librarySource, thrownException);
+      throw new AnalysisException('<rethrow>', thrownException);
+    }
+    lintMap.forEach((Source unitSource, List<AnalysisError> lints) {
+      DartEntry dartEntry = _cache.get(unitSource);
+      if (unitSource == librarySource) {
+        libraryEntry = dartEntry;
+      }
+      if (thrownException == null) {
+        dartEntry.setValueInLibrary(DartEntry.LINTS, librarySource, lints);
+        ChangeNoticeImpl notice = getNotice(unitSource);
+        LineInfo lineInfo = dartEntry.getValue(SourceEntry.LINE_INFO);
+        notice.setErrors(dartEntry.allErrors, lineInfo);
+      } else {
+        dartEntry.recordLintErrorInLibrary(librarySource, thrownException);
+      }
+    });
+    if (thrownException != null) {
+      throw new AnalysisException('<rethrow>', thrownException);
+    }
+    return libraryEntry;
+  }
+
+  /**
+   * Record the results produced by performing a [task] and return the cache
+   * entry associated with the results.
+   */
+  SourceEntry _recordGetContentsTask(GetContentTask task) {
+    if (!task.isComplete) {
+      return null;
+    }
+    Source source = task.source;
+    SourceEntry sourceEntry = _cache.get(source);
+    CaughtException thrownException = task.exception;
+    if (thrownException != null) {
+      sourceEntry.recordContentError(thrownException);
+      {
+        sourceEntry.setValue(SourceEntry.CONTENT_ERRORS, task.errors);
+        ChangeNoticeImpl notice = getNotice(source);
+        notice.setErrors(sourceEntry.allErrors, null);
+      }
+      _workManager.remove(source);
+      throw new AnalysisException('<rethrow>', thrownException);
+    }
+    sourceEntry.modificationTime = task.modificationTime;
+    sourceEntry.setValue(SourceEntry.CONTENT, task.content);
+    return sourceEntry;
+  }
+
+  /**
+   * Record the results produced by performing a [task] and return the cache
+   * entry associated with the results.
+   */
+  DartEntry _recordIncrementalAnalysisTaskResults(
+      IncrementalAnalysisTask task) {
+    CompilationUnit unit = task.compilationUnit;
+    if (unit != null) {
+      ChangeNoticeImpl notice = getNotice(task.source);
+      notice.resolvedDartUnit = unit;
+      _incrementalAnalysisCache =
+          IncrementalAnalysisCache.cacheResult(task.cache, unit);
+    }
+    return null;
+  }
+
+  /**
+   * Record the results produced by performing a [task] and return the cache
+   * entry associated with the results.
+   */
+  DartEntry _recordParseDartTaskResults(ParseDartTask task) {
+    Source source = task.source;
+    DartEntry dartEntry = _cache.get(source);
+    _removeFromParts(source, dartEntry);
+    CaughtException thrownException = task.exception;
+    if (thrownException != null) {
+      _removeFromParts(source, dartEntry);
+      dartEntry.recordParseError(thrownException);
+      _cache.removedAst(source);
+      throw new AnalysisException('<rethrow>', thrownException);
+    }
+    if (task.hasNonPartOfDirective) {
+      dartEntry.setValue(DartEntry.SOURCE_KIND, SourceKind.LIBRARY);
+      dartEntry.containingLibrary = source;
+      _workManager.add(source, SourcePriority.LIBRARY);
+    } else if (task.hasPartOfDirective) {
+      dartEntry.setValue(DartEntry.SOURCE_KIND, SourceKind.PART);
+      dartEntry.removeContainingLibrary(source);
+      _workManager.add(source, SourcePriority.NORMAL_PART);
+    } else {
+      // The file contains no directives.
+      List<Source> containingLibraries = dartEntry.containingLibraries;
+      if (containingLibraries.length > 1 ||
+          (containingLibraries.length == 1 &&
+              containingLibraries[0] != source)) {
+        dartEntry.setValue(DartEntry.SOURCE_KIND, SourceKind.PART);
+        dartEntry.removeContainingLibrary(source);
+        _workManager.add(source, SourcePriority.NORMAL_PART);
+      } else {
+        dartEntry.setValue(DartEntry.SOURCE_KIND, SourceKind.LIBRARY);
+        dartEntry.containingLibrary = source;
+        _workManager.add(source, SourcePriority.LIBRARY);
+      }
+    }
+    List<Source> newParts = task.includedSources;
+    for (int i = 0; i < newParts.length; i++) {
+      Source partSource = newParts[i];
+      DartEntry partEntry = _getReadableDartEntry(partSource);
+      if (partEntry != null && !identical(partEntry, dartEntry)) {
+        // TODO(brianwilkerson) Change the kind of the "part" if it was marked
+        // as a library and it has no directives.
+        partEntry.addContainingLibrary(source);
+      }
+    }
+    dartEntry.setValue(DartEntry.PARSED_UNIT, task.compilationUnit);
+    dartEntry.setValue(DartEntry.PARSE_ERRORS, task.errors);
+    dartEntry.setValue(DartEntry.EXPORTED_LIBRARIES, task.exportedSources);
+    dartEntry.setValue(DartEntry.IMPORTED_LIBRARIES, task.importedSources);
+    dartEntry.setValue(DartEntry.INCLUDED_PARTS, newParts);
+    _cache.storedAst(source);
+    ChangeNoticeImpl notice = getNotice(source);
+    if (notice.resolvedDartUnit == null) {
+      notice.parsedDartUnit = task.compilationUnit;
+    }
+    notice.setErrors(dartEntry.allErrors, task.lineInfo);
+    // Verify that the incrementally parsed and resolved unit in the incremental
+    // cache is structurally equivalent to the fully parsed unit
+    _incrementalAnalysisCache = IncrementalAnalysisCache.verifyStructure(
+        _incrementalAnalysisCache, source, task.compilationUnit);
+    return dartEntry;
+  }
+
+  /**
+   * Record the results produced by performing a [task] and return the cache
+   * entry associated with the results.
+   */
+  HtmlEntry _recordParseHtmlTaskResults(ParseHtmlTask task) {
+    Source source = task.source;
+    HtmlEntry htmlEntry = _cache.get(source);
+    CaughtException thrownException = task.exception;
+    if (thrownException != null) {
+      htmlEntry.recordParseError(thrownException);
+      _cache.removedAst(source);
+      throw new AnalysisException('<rethrow>', thrownException);
+    }
+    LineInfo lineInfo = task.lineInfo;
+    htmlEntry.setValue(SourceEntry.LINE_INFO, lineInfo);
+    htmlEntry.setValue(HtmlEntry.PARSED_UNIT, task.htmlUnit);
+    htmlEntry.setValue(HtmlEntry.PARSE_ERRORS, task.errors);
+    htmlEntry.setValue(
+        HtmlEntry.REFERENCED_LIBRARIES, task.referencedLibraries);
+    _cache.storedAst(source);
+    ChangeNoticeImpl notice = getNotice(source);
+    notice.setErrors(htmlEntry.allErrors, lineInfo);
+    return htmlEntry;
+  }
+
+  /**
+   * Record the results produced by performing a [task] and return the cache
+   * entry associated with the results.
+   */
+  DartEntry _recordResolveDartUnitTaskResults(ResolveDartUnitTask task) {
+    Source unitSource = task.source;
+    DartEntry dartEntry = _cache.get(unitSource);
+    Source librarySource = task.librarySource;
+    CaughtException thrownException = task.exception;
+    if (thrownException != null) {
+      dartEntry.recordResolutionErrorInLibrary(librarySource, thrownException);
+      _cache.removedAst(unitSource);
+      throw new AnalysisException('<rethrow>', thrownException);
+    }
+    dartEntry.setValueInLibrary(
+        DartEntry.RESOLVED_UNIT, librarySource, task.resolvedUnit);
+    _cache.storedAst(unitSource);
+    return dartEntry;
+  }
+
+  /**
+   * Record the results produced by performing a [task] and return the cache
+   * entry associated with the results.
+   */
+  HtmlEntry _recordResolveHtmlTaskResults(ResolveHtmlTask task) {
+    Source source = task.source;
+    HtmlEntry htmlEntry = _cache.get(source);
+    CaughtException thrownException = task.exception;
+    if (thrownException != null) {
+      htmlEntry.recordResolutionError(thrownException);
+      _cache.removedAst(source);
+      throw new AnalysisException('<rethrow>', thrownException);
+    }
+    htmlEntry.setState(HtmlEntry.PARSED_UNIT, CacheState.FLUSHED);
+    htmlEntry.setValue(HtmlEntry.RESOLVED_UNIT, task.resolvedUnit);
+    htmlEntry.setValue(HtmlEntry.ELEMENT, task.element);
+    htmlEntry.setValue(HtmlEntry.RESOLUTION_ERRORS, task.resolutionErrors);
+    _cache.storedAst(source);
+    ChangeNoticeImpl notice = getNotice(source);
+    notice.resolvedHtmlUnit = task.resolvedUnit;
+    LineInfo lineInfo = htmlEntry.getValue(SourceEntry.LINE_INFO);
+    notice.setErrors(htmlEntry.allErrors, lineInfo);
+    return htmlEntry;
+  }
+
+  /**
+   * Record the results produced by performing a [task] and return the cache
+   * entry associated with the results.
+   */
+  DartEntry _recordScanDartTaskResults(ScanDartTask task) {
+    Source source = task.source;
+    DartEntry dartEntry = _cache.get(source);
+    CaughtException thrownException = task.exception;
+    if (thrownException != null) {
+      _removeFromParts(source, dartEntry);
+      dartEntry.recordScanError(thrownException);
+      _cache.removedAst(source);
+      throw new AnalysisException('<rethrow>', thrownException);
+    }
+    LineInfo lineInfo = task.lineInfo;
+    dartEntry.setValue(SourceEntry.LINE_INFO, lineInfo);
+    dartEntry.setValue(DartEntry.TOKEN_STREAM, task.tokenStream);
+    dartEntry.setValue(DartEntry.SCAN_ERRORS, task.errors);
+    _cache.storedAst(source);
+    ChangeNoticeImpl notice = getNotice(source);
+    notice.setErrors(dartEntry.allErrors, lineInfo);
+    return dartEntry;
+  }
+
+  void _removeFromCache(Source source) {
+    SourceEntry entry = _cache.remove(source);
+    if (entry != null && !entry.explicitlyAdded) {
+      _implicitAnalysisEventsController
+          .add(new ImplicitAnalysisEvent(source, false));
+    }
+  }
+
+  /**
+   * Remove the given [librarySource] from the list of containing libraries for
+   * all of the parts referenced by the given [dartEntry].
+   */
+  void _removeFromParts(Source librarySource, DartEntry dartEntry) {
+    List<Source> oldParts = dartEntry.getValue(DartEntry.INCLUDED_PARTS);
+    for (int i = 0; i < oldParts.length; i++) {
+      Source partSource = oldParts[i];
+      DartEntry partEntry = _getReadableDartEntry(partSource);
+      if (partEntry != null && !identical(partEntry, dartEntry)) {
+        partEntry.removeContainingLibrary(librarySource);
+        if (partEntry.containingLibraries.length == 0 && !exists(partSource)) {
+          _removeFromCache(partSource);
+        }
+      }
+    }
+  }
+
+  /**
+   * Remove the given libraries that are keys in the given map from the list of
+   * containing libraries for each of the parts in the corresponding value.
+   */
+  void _removeFromPartsUsingMap(HashMap<Source, List<Source>> oldPartMap) {
+    oldPartMap.forEach((Source librarySource, List<Source> oldParts) {
+      for (int i = 0; i < oldParts.length; i++) {
+        Source partSource = oldParts[i];
+        if (partSource != librarySource) {
+          DartEntry partEntry = _getReadableDartEntry(partSource);
+          if (partEntry != null) {
+            partEntry.removeContainingLibrary(librarySource);
+            if (partEntry.containingLibraries.length == 0 &&
+                !exists(partSource)) {
+              _removeFromCache(partSource);
+            }
+          }
+        }
+      }
+    });
+  }
+
+  /**
+   * Remove the given [source] from the priority order if it is in the list.
+   */
+  void _removeFromPriorityOrder(Source source) {
+    int count = _priorityOrder.length;
+    List<Source> newOrder = new List<Source>();
+    for (int i = 0; i < count; i++) {
+      if (_priorityOrder[i] != source) {
+        newOrder.add(_priorityOrder[i]);
+      }
+    }
+    if (newOrder.length < count) {
+      analysisPriorityOrder = newOrder;
+    }
+  }
+
+  /**
+   * Create an entry for the newly added [source] and invalidate any sources
+   * that referenced the source before it existed.
+   */
+  void _sourceAvailable(Source source) {
+    // TODO(brianwilkerson) This method needs to check whether the source was
+    // previously being implicitly analyzed. If so, the cache entry needs to be
+    // update to reflect the new status and an event needs to be generated to
+    // inform clients that it is no longer being implicitly analyzed.
+    SourceEntry sourceEntry = _cache.get(source);
+    if (sourceEntry == null) {
+      sourceEntry = _createSourceEntry(source, true);
+    } else {
+      _propagateInvalidation(source, sourceEntry);
+      sourceEntry = _cache.get(source);
+    }
+    if (sourceEntry is HtmlEntry) {
+      _workManager.add(source, SourcePriority.HTML);
+    } else if (sourceEntry is DartEntry) {
+      _workManager.add(source, _computePriority(sourceEntry));
+    }
+  }
+
+  /**
+   * Invalidate the [source] that was changed and any sources that referenced
+   * the source before it existed.
+   */
+  void _sourceChanged(Source source) {
+    SourceEntry sourceEntry = _cache.get(source);
+    // If the source is removed, we don't care about it.
+    if (sourceEntry == null) {
+      return;
+    }
+    // Check if the content of the source is the same as it was the last time.
+    String sourceContent = sourceEntry.getValue(SourceEntry.CONTENT);
+    if (sourceContent != null) {
+      sourceEntry.setState(SourceEntry.CONTENT, CacheState.FLUSHED);
+      try {
+        TimestampedData<String> fileContents = getContents(source);
+        if (fileContents.data == sourceContent) {
+          return;
+        }
+      } catch (e) {}
+    }
+    // We have to invalidate the cache.
+    _propagateInvalidation(source, sourceEntry);
+  }
+
+  /**
+   * Record that the give [source] has been deleted.
+   */
+  void _sourceDeleted(Source source) {
+    SourceEntry sourceEntry = _cache.get(source);
+    if (sourceEntry is HtmlEntry) {
+      HtmlEntry htmlEntry = sourceEntry;
+      htmlEntry.recordContentError(new CaughtException(
+          new AnalysisException("This source was marked as being deleted"),
+          null));
+    } else if (sourceEntry is DartEntry) {
+      DartEntry dartEntry = sourceEntry;
+      HashSet<Source> libraries = new HashSet<Source>();
+      for (Source librarySource in getLibrariesContaining(source)) {
+        libraries.add(librarySource);
+        for (Source dependentLibrary
+            in getLibrariesDependingOn(librarySource)) {
+          libraries.add(dependentLibrary);
+        }
+      }
+      for (Source librarySource in libraries) {
+        _invalidateLibraryResolution(librarySource);
+      }
+      dartEntry.recordContentError(new CaughtException(
+          new AnalysisException("This source was marked as being deleted"),
+          null));
+    }
+    _workManager.remove(source);
+    _removeFromPriorityOrder(source);
+  }
+
+  /**
+   * Record that the given [source] has been removed.
+   */
+  void _sourceRemoved(Source source) {
+    SourceEntry sourceEntry = _cache.get(source);
+    if (sourceEntry is HtmlEntry) {} else if (sourceEntry is DartEntry) {
+      HashSet<Source> libraries = new HashSet<Source>();
+      for (Source librarySource in getLibrariesContaining(source)) {
+        libraries.add(librarySource);
+        for (Source dependentLibrary
+            in getLibrariesDependingOn(librarySource)) {
+          libraries.add(dependentLibrary);
+        }
+      }
+      for (Source librarySource in libraries) {
+        _invalidateLibraryResolution(librarySource);
+      }
+    }
+    _removeFromCache(source);
+    _workManager.remove(source);
+    _removeFromPriorityOrder(source);
+  }
+
+  /**
+   * TODO(scheglov) A hackish, limited incremental resolution implementation.
+   */
+  bool _tryPoorMansIncrementalResolution(Source unitSource, String newCode) {
+    return PerformanceStatistics.incrementalAnalysis.makeCurrentWhile(() {
+      incrementalResolutionValidation_lastUnitSource = null;
+      incrementalResolutionValidation_lastLibrarySource = null;
+      incrementalResolutionValidation_lastUnit = null;
+      // prepare the entry
+      DartEntry dartEntry = _cache.get(unitSource);
+      if (dartEntry == null) {
+        return false;
+      }
+      // prepare the (only) library source
+      List<Source> librarySources = getLibrariesContaining(unitSource);
+      if (librarySources.length != 1) {
+        return false;
+      }
+      Source librarySource = librarySources[0];
+      // prepare the library element
+      LibraryElement libraryElement = getLibraryElement(librarySource);
+      if (libraryElement == null) {
+        return false;
+      }
+      // prepare the existing unit
+      CompilationUnit oldUnit =
+          getResolvedCompilationUnit2(unitSource, librarySource);
+      if (oldUnit == null) {
+        return false;
+      }
+      // do resolution
+      Stopwatch perfCounter = new Stopwatch()..start();
+      PoorMansIncrementalResolver resolver = new PoorMansIncrementalResolver(
+          typeProvider,
+          unitSource,
+          getReadableSourceEntryOrNull(unitSource),
+          null,
+          null,
+          oldUnit,
+          analysisOptions.incrementalApi,
+          analysisOptions);
+      bool success = resolver.resolve(newCode);
+      AnalysisEngine.instance.instrumentationService.logPerformance(
+          AnalysisPerformanceKind.INCREMENTAL,
+          perfCounter,
+          'success=$success,context_id=$_id,code_length=${newCode.length}');
+      if (!success) {
+        return false;
+      }
+      // if validation, remember the result, but throw it away
+      if (analysisOptions.incrementalValidation) {
+        incrementalResolutionValidation_lastUnitSource = oldUnit.element.source;
+        incrementalResolutionValidation_lastLibrarySource =
+            oldUnit.element.library.source;
+        incrementalResolutionValidation_lastUnit = oldUnit;
+        return false;
+      }
+      // prepare notice
+      {
+        LineInfo lineInfo = getLineInfo(unitSource);
+        ChangeNoticeImpl notice = getNotice(unitSource);
+        notice.resolvedDartUnit = oldUnit;
+        notice.setErrors(dartEntry.allErrors, lineInfo);
+      }
+      // OK
+      return true;
+    });
+  }
+
+  void _validateLastIncrementalResolutionResult() {
+    if (incrementalResolutionValidation_lastUnitSource == null ||
+        incrementalResolutionValidation_lastLibrarySource == null ||
+        incrementalResolutionValidation_lastUnit == null) {
+      return;
+    }
+    CompilationUnit fullUnit = getResolvedCompilationUnit2(
+        incrementalResolutionValidation_lastUnitSource,
+        incrementalResolutionValidation_lastLibrarySource);
+    if (fullUnit != null) {
+      try {
+        assertSameResolution(
+            incrementalResolutionValidation_lastUnit, fullUnit);
+      } on IncrementalResolutionMismatch catch (mismatch, stack) {
+        String failure = mismatch.message;
+        String message =
+            'Incremental resolution mismatch:\n$failure\nat\n$stack';
+        AnalysisEngine.instance.logger.logError(message);
+      }
+    }
+    incrementalResolutionValidation_lastUnitSource = null;
+    incrementalResolutionValidation_lastLibrarySource = null;
+    incrementalResolutionValidation_lastUnit = null;
+  }
+}
+
+/**
+ * An object used by an analysis context to record the results of a task.
+ */
+class AnalysisContextImpl_AnalysisTaskResultRecorder
+    implements AnalysisTaskVisitor<SourceEntry> {
+  final AnalysisContextImpl AnalysisContextImpl_this;
+
+  AnalysisContextImpl_AnalysisTaskResultRecorder(this.AnalysisContextImpl_this);
+
+  @override
+  DartEntry visitGenerateDartErrorsTask(GenerateDartErrorsTask task) =>
+      AnalysisContextImpl_this._recordGenerateDartErrorsTask(task);
+
+  @override
+  DartEntry visitGenerateDartHintsTask(GenerateDartHintsTask task) =>
+      AnalysisContextImpl_this._recordGenerateDartHintsTask(task);
+
+  @override
+  DartEntry visitGenerateDartLintsTask(GenerateDartLintsTask task) =>
+      AnalysisContextImpl_this._recordGenerateDartLintsTask(task);
+
+  @override
+  SourceEntry visitGetContentTask(GetContentTask task) =>
+      AnalysisContextImpl_this._recordGetContentsTask(task);
+
+  @override
+  DartEntry visitIncrementalAnalysisTask(IncrementalAnalysisTask task) =>
+      AnalysisContextImpl_this._recordIncrementalAnalysisTaskResults(task);
+
+  @override
+  DartEntry visitParseDartTask(ParseDartTask task) =>
+      AnalysisContextImpl_this._recordParseDartTaskResults(task);
+
+  @override
+  HtmlEntry visitParseHtmlTask(ParseHtmlTask task) =>
+      AnalysisContextImpl_this._recordParseHtmlTaskResults(task);
+
+  @override
+  DartEntry visitResolveDartLibraryCycleTask(
+          ResolveDartLibraryCycleTask task) =>
+      AnalysisContextImpl_this.recordResolveDartLibraryCycleTaskResults(task);
+
+  @override
+  DartEntry visitResolveDartLibraryTask(ResolveDartLibraryTask task) =>
+      AnalysisContextImpl_this.recordResolveDartLibraryTaskResults(task);
+
+  @override
+  DartEntry visitResolveDartUnitTask(ResolveDartUnitTask task) =>
+      AnalysisContextImpl_this._recordResolveDartUnitTaskResults(task);
+
+  @override
+  HtmlEntry visitResolveHtmlTask(ResolveHtmlTask task) =>
+      AnalysisContextImpl_this._recordResolveHtmlTaskResults(task);
+
+  @override
+  DartEntry visitScanDartTask(ScanDartTask task) =>
+      AnalysisContextImpl_this._recordScanDartTaskResults(task);
+}
+
+class AnalysisContextImpl_ContextRetentionPolicy
+    implements CacheRetentionPolicy {
+  final AnalysisContextImpl AnalysisContextImpl_this;
+
+  AnalysisContextImpl_ContextRetentionPolicy(this.AnalysisContextImpl_this);
+
+  @override
+  RetentionPriority getAstPriority(Source source, SourceEntry sourceEntry) {
+    int priorityCount = AnalysisContextImpl_this._priorityOrder.length;
+    for (int i = 0; i < priorityCount; i++) {
+      if (source == AnalysisContextImpl_this._priorityOrder[i]) {
+        return RetentionPriority.HIGH;
+      }
+    }
+    if (AnalysisContextImpl_this._neededForResolution != null &&
+        AnalysisContextImpl_this._neededForResolution.contains(source)) {
+      return RetentionPriority.HIGH;
+    }
+    if (sourceEntry is DartEntry) {
+      DartEntry dartEntry = sourceEntry;
+      if (_astIsNeeded(dartEntry)) {
+        return RetentionPriority.MEDIUM;
+      }
+    }
+    return RetentionPriority.LOW;
+  }
+
+  bool _astIsNeeded(DartEntry dartEntry) =>
+      dartEntry.hasInvalidData(DartEntry.HINTS) ||
+          dartEntry.hasInvalidData(DartEntry.LINTS) ||
+          dartEntry.hasInvalidData(DartEntry.VERIFICATION_ERRORS) ||
+          dartEntry.hasInvalidData(DartEntry.RESOLUTION_ERRORS);
+}
+
+/**
+ * An object used to construct a list of the libraries that must be resolved
+ * together in order to resolve any one of the libraries.
+ */
+class AnalysisContextImpl_CycleBuilder {
+  final AnalysisContextImpl AnalysisContextImpl_this;
+
+  /**
+   * A table mapping the sources of the defining compilation units of libraries
+   * to the representation of the library that has the information needed to
+   * resolve the library.
+   */
+  HashMap<Source, ResolvableLibrary> _libraryMap =
+      new HashMap<Source, ResolvableLibrary>();
+
+  /**
+   * The dependency graph used to compute the libraries in the cycle.
+   */
+  DirectedGraph<ResolvableLibrary> _dependencyGraph;
+
+  /**
+   * A list containing the libraries that are ready to be resolved.
+   */
+  List<ResolvableLibrary> _librariesInCycle;
+
+  /**
+   * The analysis task that needs to be performed before the cycle of libraries
+   * can be resolved, or `null` if the libraries are ready to be resolved.
+   */
+  AnalysisContextImpl_TaskData _taskData;
+
+  /**
+   * Initialize a newly created cycle builder.
+   */
+  AnalysisContextImpl_CycleBuilder(this.AnalysisContextImpl_this) : super();
+
+  /**
+   * Return a list containing the libraries that are ready to be resolved
+   * (assuming that [getTaskData] returns `null`).
+   */
+  List<ResolvableLibrary> get librariesInCycle => _librariesInCycle;
+
+  /**
+   * Return a representation of an analysis task that needs to be performed
+   * before the cycle of libraries can be resolved, or `null` if the libraries
+   * are ready to be resolved.
+   */
+  AnalysisContextImpl_TaskData get taskData => _taskData;
+
+  /**
+   * Compute a list of the libraries that need to be resolved together in orde
+   *  to resolve the given [librarySource].
+   */
+  void computeCycleContaining(Source librarySource) {
+    //
+    // Create the object representing the library being resolved.
+    //
+    ResolvableLibrary targetLibrary = _createLibrary(librarySource);
+    //
+    // Compute the set of libraries that need to be resolved together.
+    //
+    _dependencyGraph = new DirectedGraph<ResolvableLibrary>();
+    _computeLibraryDependencies(targetLibrary);
+    if (_taskData != null) {
+      return;
+    }
+    _librariesInCycle = _dependencyGraph.findCycleContaining(targetLibrary);
+    //
+    // Ensure that all of the data needed to resolve them has been computed.
+    //
+    _ensureImportsAndExports();
+    if (_taskData != null) {
+      // At least one imported library needs to be resolved before the target
+      // library.
+      AnalysisTask task = _taskData.task;
+      if (task is ResolveDartLibraryTask) {
+        AnalysisContextImpl_this._workManager
+            .addFirst(task.librarySource, SourcePriority.LIBRARY);
+      }
+      return;
+    }
+    _computePartsInCycle(librarySource);
+    if (_taskData != null) {
+      // At least one part needs to be parsed.
+      return;
+    }
+    // All of the AST's necessary to perform a resolution of the library cycle
+    // have been gathered, so it is no longer necessary to retain them in the
+    // cache.
+    AnalysisContextImpl_this._neededForResolution = null;
+  }
+
+  bool _addDependency(ResolvableLibrary dependant, Source dependency,
+      List<ResolvableLibrary> dependencyList) {
+    if (dependant.librarySource == dependency) {
+      // Don't add a dependency of a library on itself; there's no point.
+      return true;
+    }
+    ResolvableLibrary importedLibrary = _libraryMap[dependency];
+    if (importedLibrary == null) {
+      importedLibrary = _createLibraryOrNull(dependency);
+      if (importedLibrary != null) {
+        _computeLibraryDependencies(importedLibrary);
+        if (_taskData != null) {
+          return false;
+        }
+      }
+    }
+    if (importedLibrary != null) {
+      if (dependencyList != null) {
+        dependencyList.add(importedLibrary);
+      }
+      _dependencyGraph.addEdge(dependant, importedLibrary);
+    }
+    return true;
+  }
+
+  /**
+   * Recursively traverse the libraries reachable from the given [library],
+   * creating instances of the class [Library] to represent them, and record the
+   * references in the library objects.
+   *
+   * Throws an [AnalysisException] if some portion of the library graph could
+   * not be traversed.
+   */
+  void _computeLibraryDependencies(ResolvableLibrary library) {
+    Source librarySource = library.librarySource;
+    DartEntry dartEntry =
+        AnalysisContextImpl_this._getReadableDartEntry(librarySource);
+    List<Source> importedSources =
+        _getSources(librarySource, dartEntry, DartEntry.IMPORTED_LIBRARIES);
+    if (_taskData != null) {
+      return;
+    }
+    List<Source> exportedSources =
+        _getSources(librarySource, dartEntry, DartEntry.EXPORTED_LIBRARIES);
+    if (_taskData != null) {
+      return;
+    }
+    _computeLibraryDependenciesFromDirectives(
+        library, importedSources, exportedSources);
+  }
+
+  /**
+   * Recursively traverse the libraries reachable from the given [library],
+   * creating instances of the class [Library] to represent them, and record the
+   * references in the library objects. The [importedSources] is a list
+   * containing the sources that are imported into the given library. The
+   * [exportedSources] is a list containing the sources that are exported from
+   * the given library.
+   */
+  void _computeLibraryDependenciesFromDirectives(ResolvableLibrary library,
+      List<Source> importedSources, List<Source> exportedSources) {
+    int importCount = importedSources.length;
+    List<ResolvableLibrary> importedLibraries = new List<ResolvableLibrary>();
+    bool explicitlyImportsCore = false;
+    bool importsAsync = false;
+    for (int i = 0; i < importCount; i++) {
+      Source importedSource = importedSources[i];
+      if (importedSource == AnalysisContextImpl_this._coreLibrarySource) {
+        explicitlyImportsCore = true;
+      } else if (importedSource ==
+          AnalysisContextImpl_this._asyncLibrarySource) {
+        importsAsync = true;
+      }
+      if (!_addDependency(library, importedSource, importedLibraries)) {
+        return;
+      }
+    }
+    library.explicitlyImportsCore = explicitlyImportsCore;
+    if (!explicitlyImportsCore) {
+      if (!_addDependency(library, AnalysisContextImpl_this._coreLibrarySource,
+          importedLibraries)) {
+        return;
+      }
+    }
+    if (!importsAsync) {
+      // Add a dependency on async to ensure that the Future element will be
+      // built before we generate errors and warnings for async methods.  Also
+      // include it in importedLibraries, so that it will be picked up by
+      // LibraryResolver2._buildLibraryMap().
+      // TODO(paulberry): this is a bit of a hack, since the async library
+      // isn't actually being imported.  Also, it's not clear whether it should
+      // be necessary: in theory, dart:core already (indirectly) imports
+      // dart:async, so if core has been built, async should have been built
+      // too.  However, removing this code causes unit test failures.
+      if (!_addDependency(library, AnalysisContextImpl_this._asyncLibrarySource,
+          importedLibraries)) {
+        return;
+      }
+    }
+    library.importedLibraries = importedLibraries;
+    int exportCount = exportedSources.length;
+    if (exportCount > 0) {
+      List<ResolvableLibrary> exportedLibraries = new List<ResolvableLibrary>();
+      for (int i = 0; i < exportCount; i++) {
+        Source exportedSource = exportedSources[i];
+        if (!_addDependency(library, exportedSource, exportedLibraries)) {
+          return;
+        }
+      }
+      library.exportedLibraries = exportedLibraries;
+    }
+  }
+
+  /**
+   * Gather the resolvable AST structures for each of the compilation units in
+   * each of the libraries in the cycle. This is done in two phases: first we
+   * ensure that we have cached an AST structure for each compilation unit, then
+   * we gather them. We split the work this way because getting the AST
+   * structures can change the state of the cache in such a way that we would
+   * have more work to do if any compilation unit didn't have a resolvable AST
+   * structure.
+   */
+  void _computePartsInCycle(Source librarySource) {
+    int count = _librariesInCycle.length;
+    List<CycleBuilder_LibraryPair> libraryData =
+        new List<CycleBuilder_LibraryPair>();
+    for (int i = 0; i < count; i++) {
+      ResolvableLibrary library = _librariesInCycle[i];
+      libraryData.add(new CycleBuilder_LibraryPair(
+          library, _ensurePartsInLibrary(library)));
+    }
+    AnalysisContextImpl_this._neededForResolution = _gatherSources(libraryData);
+    if (AnalysisContextImpl._TRACE_PERFORM_TASK) {
+      print(
+          "  preserve resolution data for ${AnalysisContextImpl_this._neededForResolution.length} sources while resolving ${librarySource.fullName}");
+    }
+    if (_taskData != null) {
+      return;
+    }
+    for (int i = 0; i < count; i++) {
+      _computePartsInLibrary(libraryData[i]);
+    }
+  }
+
+  /**
+   * Gather the resolvable compilation units for each of the compilation units
+   * in the library represented by the [libraryPair].
+   */
+  void _computePartsInLibrary(CycleBuilder_LibraryPair libraryPair) {
+    ResolvableLibrary library = libraryPair.library;
+    List<CycleBuilder_SourceEntryPair> entryPairs = libraryPair.entryPairs;
+    int count = entryPairs.length;
+    List<ResolvableCompilationUnit> units =
+        new List<ResolvableCompilationUnit>(count);
+    for (int i = 0; i < count; i++) {
+      CycleBuilder_SourceEntryPair entryPair = entryPairs[i];
+      Source source = entryPair.source;
+      DartEntry dartEntry = entryPair.entry;
+      units[i] = new ResolvableCompilationUnit(
+          source, dartEntry.resolvableCompilationUnit);
+    }
+    library.resolvableCompilationUnits = units;
+  }
+
+  /**
+   * Create an object to represent the information about the library defined by
+   * the compilation unit with the given [librarySource].
+   */
+  ResolvableLibrary _createLibrary(Source librarySource) {
+    ResolvableLibrary library = new ResolvableLibrary(librarySource);
+    SourceEntry sourceEntry =
+        AnalysisContextImpl_this._cache.get(librarySource);
+    if (sourceEntry is DartEntry) {
+      LibraryElementImpl libraryElement =
+          sourceEntry.getValue(DartEntry.ELEMENT) as LibraryElementImpl;
+      if (libraryElement != null) {
+        library.libraryElement = libraryElement;
+      }
+    }
+    _libraryMap[librarySource] = library;
+    return library;
+  }
+
+  /**
+   * Create an object to represent the information about the library defined by
+   * the compilation unit with the given [librarySource].
+   */
+  ResolvableLibrary _createLibraryOrNull(Source librarySource) {
+    ResolvableLibrary library = new ResolvableLibrary(librarySource);
+    SourceEntry sourceEntry =
+        AnalysisContextImpl_this._cache.get(librarySource);
+    if (sourceEntry is DartEntry) {
+      LibraryElementImpl libraryElement =
+          sourceEntry.getValue(DartEntry.ELEMENT) as LibraryElementImpl;
+      if (libraryElement != null) {
+        library.libraryElement = libraryElement;
+      }
+    }
+    _libraryMap[librarySource] = library;
+    return library;
+  }
+
+  /**
+   * Ensure that the given [library] has an element model built for it. If
+   * another task needs to be executed first in order to build the element
+   * model, that task is placed in [taskData].
+   */
+  void _ensureElementModel(ResolvableLibrary library) {
+    Source librarySource = library.librarySource;
+    DartEntry libraryEntry =
+        AnalysisContextImpl_this._getReadableDartEntry(librarySource);
+    if (libraryEntry != null &&
+        libraryEntry.getState(DartEntry.PARSED_UNIT) != CacheState.ERROR) {
+      AnalysisContextImpl_this._workManager
+          .addFirst(librarySource, SourcePriority.LIBRARY);
+      if (_taskData == null) {
+        _taskData = AnalysisContextImpl_this._createResolveDartLibraryTask(
+            librarySource, libraryEntry);
+      }
+    }
+  }
+
+  /**
+   * Ensure that all of the libraries that are exported by the given [library]
+   * (but are not themselves in the cycle) have element models built for them.
+   * If another task needs to be executed first in order to build the element
+   * model, that task is placed in [taskData].
+   */
+  void _ensureExports(
+      ResolvableLibrary library, HashSet<Source> visitedLibraries) {
+    List<ResolvableLibrary> dependencies = library.exports;
+    int dependencyCount = dependencies.length;
+    for (int i = 0; i < dependencyCount; i++) {
+      ResolvableLibrary dependency = dependencies[i];
+      if (!_librariesInCycle.contains(dependency) &&
+          visitedLibraries.add(dependency.librarySource)) {
+        if (dependency.libraryElement == null) {
+          _ensureElementModel(dependency);
+        } else {
+          _ensureExports(dependency, visitedLibraries);
+        }
+        if (_taskData != null) {
+          return;
+        }
+      }
+    }
+  }
+
+  /**
+   * Ensure that all of the libraries that are exported by the given [library]
+   * (but are not themselves in the cycle) have element models built for them.
+   * If another task needs to be executed first in order to build the element
+   * model, that task is placed in [taskData].
+   */
+  void _ensureImports(ResolvableLibrary library) {
+    List<ResolvableLibrary> dependencies = library.imports;
+    int dependencyCount = dependencies.length;
+    for (int i = 0; i < dependencyCount; i++) {
+      ResolvableLibrary dependency = dependencies[i];
+      if (!_librariesInCycle.contains(dependency) &&
+          dependency.libraryElement == null) {
+        _ensureElementModel(dependency);
+        if (_taskData != null) {
+          return;
+        }
+      }
+    }
+  }
+
+  /**
+   * Ensure that all of the libraries that are either imported or exported by
+   * libraries in the cycle (but are not themselves in the cycle) have element
+   * models built for them.
+   */
+  void _ensureImportsAndExports() {
+    HashSet<Source> visitedLibraries = new HashSet<Source>();
+    int libraryCount = _librariesInCycle.length;
+    for (int i = 0; i < libraryCount; i++) {
+      ResolvableLibrary library = _librariesInCycle[i];
+      _ensureImports(library);
+      if (_taskData != null) {
+        return;
+      }
+      _ensureExports(library, visitedLibraries);
+      if (_taskData != null) {
+        return;
+      }
+    }
+  }
+
+  /**
+   * Ensure that there is a resolvable compilation unit available for all of the
+   * compilation units in the given [library].
+   */
+  List<CycleBuilder_SourceEntryPair> _ensurePartsInLibrary(
+      ResolvableLibrary library) {
+    List<CycleBuilder_SourceEntryPair> pairs =
+        new List<CycleBuilder_SourceEntryPair>();
+    Source librarySource = library.librarySource;
+    DartEntry libraryEntry =
+        AnalysisContextImpl_this._getReadableDartEntry(librarySource);
+    if (libraryEntry == null) {
+      throw new AnalysisException(
+          "Cannot find entry for ${librarySource.fullName}");
+    } else if (libraryEntry.getState(DartEntry.PARSED_UNIT) ==
+        CacheState.ERROR) {
+      String message =
+          "Cannot compute parsed unit for ${librarySource.fullName}";
+      CaughtException exception = libraryEntry.exception;
+      if (exception == null) {
+        throw new AnalysisException(message);
+      }
+      throw new AnalysisException(
+          message, new CaughtException(exception, null));
+    }
+    _ensureResolvableCompilationUnit(librarySource, libraryEntry);
+    pairs.add(new CycleBuilder_SourceEntryPair(librarySource, libraryEntry));
+    List<Source> partSources =
+        _getSources(librarySource, libraryEntry, DartEntry.INCLUDED_PARTS);
+    int count = partSources.length;
+    for (int i = 0; i < count; i++) {
+      Source partSource = partSources[i];
+      DartEntry partEntry =
+          AnalysisContextImpl_this._getReadableDartEntry(partSource);
+      if (partEntry != null &&
+          partEntry.getState(DartEntry.PARSED_UNIT) != CacheState.ERROR) {
+        _ensureResolvableCompilationUnit(partSource, partEntry);
+        pairs.add(new CycleBuilder_SourceEntryPair(partSource, partEntry));
+      }
+    }
+    return pairs;
+  }
+
+  /**
+   * Ensure that there is a resolvable compilation unit available for the given
+   * [source].
+   */
+  void _ensureResolvableCompilationUnit(Source source, DartEntry dartEntry) {
+    // The entry will be null if the source represents a non-Dart file.
+    if (dartEntry != null && !dartEntry.hasResolvableCompilationUnit) {
+      if (_taskData == null) {
+        _taskData =
+            AnalysisContextImpl_this._createParseDartTask(source, dartEntry);
+      }
+    }
+  }
+
+  HashSet<Source> _gatherSources(List<CycleBuilder_LibraryPair> libraryData) {
+    int libraryCount = libraryData.length;
+    HashSet<Source> sources = new HashSet<Source>();
+    for (int i = 0; i < libraryCount; i++) {
+      List<CycleBuilder_SourceEntryPair> entryPairs = libraryData[i].entryPairs;
+      int entryCount = entryPairs.length;
+      for (int j = 0; j < entryCount; j++) {
+        sources.add(entryPairs[j].source);
+      }
+    }
+    return sources;
+  }
+
+  /**
+   * Return the sources described by the given [descriptor].
+   */
+  List<Source> _getSources(Source source, DartEntry dartEntry,
+      DataDescriptor<List<Source>> descriptor) {
+    if (dartEntry == null) {
+      return Source.EMPTY_LIST;
+    }
+    CacheState exportState = dartEntry.getState(descriptor);
+    if (exportState == CacheState.ERROR) {
+      return Source.EMPTY_LIST;
+    } else if (exportState != CacheState.VALID) {
+      if (_taskData == null) {
+        _taskData =
+            AnalysisContextImpl_this._createParseDartTask(source, dartEntry);
+      }
+      return Source.EMPTY_LIST;
+    }
+    return dartEntry.getValue(descriptor);
+  }
+}
+
+/**
+ * Information about the next task to be performed. Each data has an implicit
+ * associated source: the source that might need to be analyzed. There are
+ * essentially three states that can be represented:
+ *
+ * * If [getTask] returns a non-`null` value, then that is the task that should
+ *   be executed to further analyze the associated source.
+ * * Otherwise, if [isBlocked] returns `true`, then there is no work that can be
+ *   done, but analysis for the associated source is not complete.
+ * * Otherwise, [getDependentSource] should return a source that needs to be
+ *   analyzed before the analysis of the associated source can be completed.
+ */
+class AnalysisContextImpl_TaskData {
+  /**
+   * The task that is to be performed.
+   */
+  final AnalysisTask task;
+
+  /**
+   * A flag indicating whether the associated source is blocked waiting for its
+   * contents to be loaded.
+   */
+  final bool _blocked;
+
+  /**
+   * Initialize a newly created data holder.
+   */
+  AnalysisContextImpl_TaskData(this.task, this._blocked);
+
+  /**
+   * Return `true` if the associated source is blocked waiting for its contents
+   * to be loaded.
+   */
+  bool get isBlocked => _blocked;
+
+  @override
+  String toString() {
+    if (task == null) {
+      return "blocked: $_blocked";
+    }
+    return task.toString();
+  }
+}
+
+/**
+ * Statistics and information about a single [AnalysisContext].
+ */
+abstract class AnalysisContextStatistics {
+  /**
+   * Return the statistics for each kind of cached data.
+   */
+  List<AnalysisContextStatistics_CacheRow> get cacheRows;
+
+  /**
+   * Return the exceptions that caused some entries to have a state of
+   * [CacheState.ERROR].
+   */
+  List<CaughtException> get exceptions;
+
+  /**
+   * Return information about each of the partitions in the cache.
+   */
+  List<AnalysisContextStatistics_PartitionData> get partitionData;
+
+  /**
+   * Return a list containing all of the sources in the cache.
+   */
+  List<Source> get sources;
+}
+
+/**
+ * Information about single piece of data in the cache.
+ */
+abstract class AnalysisContextStatistics_CacheRow {
+  /**
+   * List of possible states which can be queried.
+   */
+  static const List<CacheState> STATES = const <CacheState>[
+    CacheState.ERROR,
+    CacheState.FLUSHED,
+    CacheState.IN_PROCESS,
+    CacheState.INVALID,
+    CacheState.VALID
+  ];
+
+  /**
+   * Return the number of entries whose state is [CacheState.ERROR].
+   */
+  int get errorCount;
+
+  /**
+   * Return the number of entries whose state is [CacheState.FLUSHED].
+   */
+  int get flushedCount;
+
+  /**
+   * Return the number of entries whose state is [CacheState.IN_PROCESS].
+   */
+  int get inProcessCount;
+
+  /**
+   * Return the number of entries whose state is [CacheState.INVALID].
+   */
+  int get invalidCount;
+
+  /**
+   * Return the name of the data represented by this object.
+   */
+  String get name;
+
+  /**
+   * Return the number of entries whose state is [CacheState.VALID].
+   */
+  int get validCount;
+
+  /**
+   * Return the number of entries whose state is [state].
+   */
+  int getCount(CacheState state);
+}
+
+/**
+ * Information about a single partition in the cache.
+ */
+abstract class AnalysisContextStatistics_PartitionData {
+  /**
+   * Return the number of entries in the partition that have an AST structure in
+   * one state or another.
+   */
+  int get astCount;
+
+  /**
+   * Return the total number of entries in the partition.
+   */
+  int get totalCount;
+}
+
+/**
+ * Implementation of the [AnalysisContextStatistics].
+ */
+class AnalysisContextStatisticsImpl implements AnalysisContextStatistics {
+  Map<String, AnalysisContextStatistics_CacheRow> _dataMap =
+      new HashMap<String, AnalysisContextStatistics_CacheRow>();
+
+  List<Source> _sources = new List<Source>();
+
+  HashSet<CaughtException> _exceptions = new HashSet<CaughtException>();
+
+  List<AnalysisContextStatistics_PartitionData> _partitionData;
+
+  @override
+  List<AnalysisContextStatistics_CacheRow> get cacheRows =>
+      _dataMap.values.toList();
+
+  @override
+  List<CaughtException> get exceptions => new List.from(_exceptions);
+
+  @override
+  List<AnalysisContextStatistics_PartitionData> get partitionData =>
+      _partitionData;
+
+  /**
+   * Set the partition data returned by this object to the given data.
+   */
+  void set partitionData(List<AnalysisContextStatistics_PartitionData> data) {
+    _partitionData = data;
+  }
+
+  @override
+  List<Source> get sources => _sources;
+
+  void addSource(Source source) {
+    _sources.add(source);
+  }
+
+  void _internalPutCacheItem(Source source, SourceEntry dartEntry,
+      DataDescriptor rowDesc, CacheState state) {
+    String rowName = rowDesc.toString();
+    AnalysisContextStatisticsImpl_CacheRowImpl row =
+        _dataMap[rowName] as AnalysisContextStatisticsImpl_CacheRowImpl;
+    if (row == null) {
+      row = new AnalysisContextStatisticsImpl_CacheRowImpl(rowName);
+      _dataMap[rowName] = row;
+    }
+    row._incState(state);
+    if (state == CacheState.ERROR) {
+      CaughtException exception = dartEntry.exception;
+      if (exception != null) {
+        _exceptions.add(exception);
+      }
+    }
+  }
+}
+
+class AnalysisContextStatisticsImpl_CacheRowImpl
+    implements AnalysisContextStatistics_CacheRow {
+  final String name;
+
+  Map<CacheState, int> _counts = <CacheState, int>{};
+
+  AnalysisContextStatisticsImpl_CacheRowImpl(this.name);
+
+  @override
+  int get errorCount => getCount(CacheState.ERROR);
+
+  @override
+  int get flushedCount => getCount(CacheState.FLUSHED);
+
+  @override
+  int get hashCode => name.hashCode;
+
+  @override
+  int get inProcessCount => getCount(CacheState.IN_PROCESS);
+
+  @override
+  int get invalidCount => getCount(CacheState.INVALID);
+
+  @override
+  int get validCount => getCount(CacheState.VALID);
+
+  @override
+  bool operator ==(Object obj) =>
+      obj is AnalysisContextStatisticsImpl_CacheRowImpl && obj.name == name;
+
+  @override
+  int getCount(CacheState state) {
+    int count = _counts[state];
+    if (count != null) {
+      return count;
+    } else {
+      return 0;
+    }
+  }
+
+  void _incState(CacheState state) {
+    if (_counts[state] == null) {
+      _counts[state] = 1;
+    } else {
+      _counts[state]++;
+    }
+  }
+}
+
+class AnalysisContextStatisticsImpl_PartitionDataImpl
+    implements AnalysisContextStatistics_PartitionData {
+  final int astCount;
+
+  final int totalCount;
+
+  AnalysisContextStatisticsImpl_PartitionDataImpl(
+      this.astCount, this.totalCount);
+}
+
+/**
+ * A representation of changes to the types of analysis that should be
+ * performed.
+ */
+class AnalysisDelta {
+  /**
+   * A mapping from source to what type of analysis should be performed on that
+   * source.
+   */
+  HashMap<Source, AnalysisLevel> _analysisMap =
+      new HashMap<Source, AnalysisLevel>();
+
+  /**
+   * Return a collection of the sources that have been added. This is equivalent
+   * to calling [getAnalysisLevels] and collecting all sources that do not have
+   * an analysis level of [AnalysisLevel.NONE].
+   */
+  List<Source> get addedSources {
+    List<Source> result = new List<Source>();
+    _analysisMap.forEach((Source source, AnalysisLevel level) {
+      if (level != AnalysisLevel.NONE) {
+        result.add(source);
+      }
+    });
+    return result;
+  }
+
+  /**
+   * Return a mapping of sources to the level of analysis that should be
+   * performed.
+   */
+  Map<Source, AnalysisLevel> get analysisLevels => _analysisMap;
+
+  /**
+   * Record that the given [source] should be analyzed at the given [level].
+   */
+  void setAnalysisLevel(Source source, AnalysisLevel level) {
+    _analysisMap[source] = level;
+  }
+
+  @override
+  String toString() {
+    StringBuffer buffer = new StringBuffer();
+    bool needsSeparator = _appendSources(buffer, false, AnalysisLevel.ALL);
+    needsSeparator =
+        _appendSources(buffer, needsSeparator, AnalysisLevel.RESOLVED);
+    _appendSources(buffer, needsSeparator, AnalysisLevel.NONE);
+    return buffer.toString();
+  }
+
+  /**
+   * Appendto the given [buffer] all sources with the given analysis [level],
+   * prefixed with a label and a separator if [needsSeparator] is `true`.
+   */
+  bool _appendSources(
+      StringBuffer buffer, bool needsSeparator, AnalysisLevel level) {
+    bool first = true;
+    _analysisMap.forEach((Source source, AnalysisLevel sourceLevel) {
+      if (sourceLevel == level) {
+        if (first) {
+          first = false;
+          if (needsSeparator) {
+            buffer.write("; ");
+          }
+          buffer.write(level);
+          buffer.write(" ");
+        } else {
+          buffer.write(", ");
+        }
+        buffer.write(source.fullName);
+      }
+    });
+    return needsSeparator || !first;
+  }
+}
+
+/**
+ * The entry point for the functionality provided by the analysis engine. There
+ * is a single instance of this class.
+ */
+class AnalysisEngine {
+  /**
+   * The suffix used for Dart source files.
+   */
+  static const String SUFFIX_DART = "dart";
+
+  /**
+   * The short suffix used for HTML files.
+   */
+  static const String SUFFIX_HTM = "htm";
+
+  /**
+   * The long suffix used for HTML files.
+   */
+  static const String SUFFIX_HTML = "html";
+
+  /**
+   * The unique instance of this class.
+   */
+  static final AnalysisEngine instance = new AnalysisEngine._();
+
+  /**
+   * The logger that should receive information about errors within the analysis
+   * engine.
+   */
+  Logger _logger = Logger.NULL;
+
+  /**
+   * The plugin that defines the extension points and extensions that are defined by
+   * command-line applications using the analysis engine.
+   */
+  final CommandLinePlugin commandLinePlugin = new CommandLinePlugin();
+
+  /**
+   * The plugin that defines the extension points and extensions that are
+   * inherently defined by the analysis engine.
+   */
+  final EnginePlugin enginePlugin = new EnginePlugin();
+
+  /***
+   * The plugin that defines the extension points and extensions that are defined
+   * by applications that want to consume options defined in the analysis
+   * options file.
+   */
+  final OptionsPlugin optionsPlugin = new OptionsPlugin();
+
+  /**
+   * The instrumentation service that is to be used by this analysis engine.
+   */
+  InstrumentationService _instrumentationService =
+      InstrumentationService.NULL_SERVICE;
+
+  /**
+   * The list of supported plugins for processing by clients.
+   */
+  List<Plugin> _supportedPlugins;
+
+  /**
+   * The partition manager being used to manage the shared partitions.
+   */
+  final PartitionManager partitionManager = new PartitionManager();
+
+  /**
+   * The partition manager being used to manage the shared partitions.
+   */
+  final newContext.PartitionManager partitionManager_new =
+      new newContext.PartitionManager();
+
+  /**
+   * A flag indicating whether the (new) task model should be used to perform
+   * analysis.
+   */
+  bool useTaskModel = false;
+
+  /**
+   * A flag indicating whether the task model should attempt to limit
+   * invalidation after a change.
+   */
+  bool limitInvalidationInTaskModel = false;
+
+  /**
+   * The task manager used to manage the tasks used to analyze code.
+   */
+  TaskManager _taskManager;
+
+  AnalysisEngine._();
+
+  /**
+   * Return the instrumentation service that is to be used by this analysis
+   * engine.
+   */
+  InstrumentationService get instrumentationService => _instrumentationService;
+
+  /**
+   * Set the instrumentation service that is to be used by this analysis engine
+   * to the given [service].
+   */
+  void set instrumentationService(InstrumentationService service) {
+    if (service == null) {
+      _instrumentationService = InstrumentationService.NULL_SERVICE;
+    } else {
+      _instrumentationService = service;
+    }
+  }
+
+  /**
+   * Return the logger that should receive information about errors within the
+   * analysis engine.
+   */
+  Logger get logger => _logger;
+
+  /**
+   * Set the logger that should receive information about errors within the
+   * analysis engine to the given [logger].
+   */
+  void set logger(Logger logger) {
+    this._logger = logger == null ? Logger.NULL : logger;
+  }
+
+  /**
+   * Return the list of supported plugins for processing by clients.
+   */
+  List<Plugin> get supportedPlugins {
+    if (_supportedPlugins == null) {
+      _supportedPlugins = <Plugin>[
+        enginePlugin,
+        commandLinePlugin,
+        optionsPlugin
+      ];
+    }
+    return _supportedPlugins;
+  }
+
+  /**
+   * Return the task manager used to manage the tasks used to analyze code.
+   */
+  TaskManager get taskManager {
+    if (_taskManager == null) {
+      if (enginePlugin.taskExtensionPoint == null) {
+        // The plugin wasn't used, so tasks are not registered.
+        new ExtensionManager().processPlugins([enginePlugin]);
+      }
+      _taskManager = new TaskManager();
+      _taskManager.addTaskDescriptors(enginePlugin.taskDescriptors);
+      // TODO(brianwilkerson) Create a way to associate different results with
+      // different file suffixes, then make this pluggable.
+      _taskManager.addGeneralResult(DART_ERRORS);
+    }
+    return _taskManager;
+  }
+
+  /**
+   * Clear any caches holding on to analysis results so that a full re-analysis
+   * will be performed the next time an analysis context is created.
+   */
+  void clearCaches() {
+    partitionManager.clearCache();
+  }
+
+  /**
+   * Create and return a new context in which analysis can be performed.
+   */
+  AnalysisContext createAnalysisContext() {
+    if (useTaskModel) {
+      return new newContext.AnalysisContextImpl();
+    }
+    return new AnalysisContextImpl();
+  }
+
+  /**
+   * Return `true` if the given [fileName] is assumed to contain Dart source
+   * code.
+   */
+  static bool isDartFileName(String fileName) {
+    if (fileName == null) {
+      return false;
+    }
+    return javaStringEqualsIgnoreCase(
+        FileNameUtilities.getExtension(fileName), SUFFIX_DART);
+  }
+
+  /**
+   * Return `true` if the given [fileName] is assumed to contain HTML.
+   */
+  static bool isHtmlFileName(String fileName) {
+    if (fileName == null) {
+      return false;
+    }
+    String extension = FileNameUtilities.getExtension(fileName);
+    return javaStringEqualsIgnoreCase(extension, SUFFIX_HTML) ||
+        javaStringEqualsIgnoreCase(extension, SUFFIX_HTM);
+  }
+}
+
+/**
+ * The analysis errors and line information for the errors.
+ */
+abstract class AnalysisErrorInfo {
+  /**
+   * Return the errors that as a result of the analysis, or `null` if there were
+   * no errors.
+   */
+  List<AnalysisError> get errors;
+
+  /**
+   * Return the line information associated with the errors, or `null` if there
+   * were no errors.
+   */
+  LineInfo get lineInfo;
+}
+
+/**
+ * The analysis errors and line info associated with a source.
+ */
+class AnalysisErrorInfoImpl implements AnalysisErrorInfo {
+  /**
+   * The analysis errors associated with a source, or `null` if there are no
+   * errors.
+   */
+  final List<AnalysisError> errors;
+
+  /**
+   * The line information associated with the errors, or `null` if there are no
+   * errors.
+   */
+  final LineInfo lineInfo;
+
+  /**
+   * Initialize an newly created error info with the given [errors] and
+   * [lineInfo].
+   */
+  AnalysisErrorInfoImpl(this.errors, this.lineInfo);
+}
+
+/**
+ * The levels at which a source can be analyzed.
+ */
+class AnalysisLevel extends Enum<AnalysisLevel> {
+  /**
+   * Indicates a source should be fully analyzed.
+   */
+  static const AnalysisLevel ALL = const AnalysisLevel('ALL', 0);
+
+  /**
+   * Indicates a source should be resolved and that errors, warnings and hints are needed.
+   */
+  static const AnalysisLevel ERRORS = const AnalysisLevel('ERRORS', 1);
+
+  /**
+   * Indicates a source should be resolved, but that errors, warnings and hints are not needed.
+   */
+  static const AnalysisLevel RESOLVED = const AnalysisLevel('RESOLVED', 2);
+
+  /**
+   * Indicates a source is not of interest to the client.
+   */
+  static const AnalysisLevel NONE = const AnalysisLevel('NONE', 3);
+
+  static const List<AnalysisLevel> values = const [ALL, ERRORS, RESOLVED, NONE];
+
+  const AnalysisLevel(String name, int ordinal) : super(name, ordinal);
+}
+
+/**
+ * An object that is listening for results being produced by an analysis
+ * context.
+ */
+abstract class AnalysisListener {
+  /**
+   * Reports that a task, described by the given [taskDescription] is about to
+   * be performed by the given [context].
+   */
+  void aboutToPerformTask(AnalysisContext context, String taskDescription);
+
+  /**
+   * Reports that the [errors] associated with the given [source] in the given
+   * [context] has been updated to the given errors. The [lineInfo] is the line
+   * information associated with the source.
+   */
+  void computedErrors(AnalysisContext context, Source source,
+      List<AnalysisError> errors, LineInfo lineInfo);
+
+  /**
+   * Reports that the given [source] is no longer included in the set of sources
+   * that are being analyzed by the given analysis [context].
+   */
+  void excludedSource(AnalysisContext context, Source source);
+
+  /**
+   * Reports that the given [source] is now included in the set of sources that
+   * are being analyzed by the given analysis [context].
+   */
+  void includedSource(AnalysisContext context, Source source);
+
+  /**
+   * Reports that the given Dart [source] was parsed in the given [context],
+   * producing the given [unit].
+   */
+  void parsedDart(AnalysisContext context, Source source, CompilationUnit unit);
+
+  /**
+   * Reports that the given HTML [source] was parsed in the given [context].
+   */
+  @deprecated
+  void parsedHtml(AnalysisContext context, Source source, ht.HtmlUnit unit);
+
+  /**
+   * Reports that the given Dart [source] was resolved in the given [context].
+   */
+  void resolvedDart(
+      AnalysisContext context, Source source, CompilationUnit unit);
+
+  /**
+   * Reports that the given HTML [source] was resolved in the given [context].
+   */
+  @deprecated
+  void resolvedHtml(AnalysisContext context, Source source, ht.HtmlUnit unit);
+}
+
+/**
+ * Futures returned by [AnalysisContext] for pending analysis results will
+ * complete with this error if it is determined that analysis results will
+ * never become available (e.g. because the requested source is not subject to
+ * analysis, or because the requested source is a part file which is not a part
+ * of any known library).
+ */
+class AnalysisNotScheduledError implements Exception {}
+
+/**
+ * A set of analysis options used to control the behavior of an analysis
+ * context.
+ */
+abstract class AnalysisOptions {
+  /**
+   * If analysis is to parse and analyze all function bodies, return `true`.
+   * If analysis is to skip all function bodies, return `false`.  If analysis
+   * is to parse and analyze function bodies in some sources and not in others,
+   * throw an exception.
+   *
+   * This getter is deprecated; consider using [analyzeFunctionBodiesPredicate]
+   * instead.
+   */
+  @deprecated // Use this.analyzeFunctionBodiesPredicate
+  bool get analyzeFunctionBodies;
+
+  /**
+   * Function that returns `true` if analysis is to parse and analyze function
+   * bodies for a given source.
+   */
+  AnalyzeFunctionBodiesPredicate get analyzeFunctionBodiesPredicate;
+
+  /**
+   * Return the maximum number of sources for which AST structures should be
+   * kept in the cache.
+   */
+  int get cacheSize;
+
+  /**
+   * Return `true` if analysis is to generate dart2js related hint results.
+   */
+  bool get dart2jsHint;
+
+  /**
+   * Return `true` if analysis is to include the new async support.
+   */
+  @deprecated // Always true
+  bool get enableAsync;
+
+  /**
+   * Return `true` if analysis is to include the new deferred loading support.
+   */
+  @deprecated // Always true
+  bool get enableDeferredLoading;
+
+  /**
+   * Return `true` if analysis is to include the new enum support.
+   */
+  @deprecated // Always true
+  bool get enableEnum;
+
+  /**
+   * Return `true` to enable generic methods (DEP 22).
+   */
+  bool get enableGenericMethods => null;
+
+  /**
+   * Return `true` to enable null-aware operators (DEP 9).
+   */
+  @deprecated // Always true
+  bool get enableNullAwareOperators;
+
+  /**
+   * Return `true` to strictly follow the specification when generating
+   * warnings on "call" methods (fixes dartbug.com/21938).
+   */
+  bool get enableStrictCallChecks;
+
+  /**
+   * Return `true` if mixins are allowed to inherit from types other than
+   * Object, and are allowed to reference `super`.
+   */
+  bool get enableSuperMixins;
+
+  /**
+   * Return `true` if errors, warnings and hints should be generated for sources
+   * that are implicitly being analyzed. The default value is `true`.
+   */
+  bool get generateImplicitErrors;
+
+  /**
+   * Return `true` if errors, warnings and hints should be generated for sources
+   * in the SDK. The default value is `false`.
+   */
+  bool get generateSdkErrors;
+
+  /**
+   * Return `true` if analysis is to generate hint results (e.g. type inference
+   * based information and pub best practices).
+   */
+  bool get hint;
+
+  /**
+   * Return `true` if incremental analysis should be used.
+   */
+  bool get incremental;
+
+  /**
+   * A flag indicating whether incremental analysis should be used for API
+   * changes.
+   */
+  bool get incrementalApi;
+
+  /**
+   * A flag indicating whether validation should be performed after incremental
+   * analysis.
+   */
+  bool get incrementalValidation;
+
+  /**
+   * Return `true` if analysis is to generate lint warnings.
+   */
+  bool get lint;
+
+  /**
+   * Return `true` if analysis is to parse comments.
+   */
+  bool get preserveComments;
+
+  /**
+   * Return `true` if strong mode analysis should be used.
+   */
+  bool get strongMode;
+}
+
+/**
+ * A set of analysis options used to control the behavior of an analysis
+ * context.
+ */
+class AnalysisOptionsImpl implements AnalysisOptions {
+  /**
+   * The maximum number of sources for which data should be kept in the cache.
+   */
+  static const int DEFAULT_CACHE_SIZE = 64;
+
+  /**
+   * The default value for enabling deferred loading.
+   */
+  @deprecated
+  static bool DEFAULT_ENABLE_DEFERRED_LOADING = true;
+
+  /**
+   * The default value for enabling enum support.
+   */
+  @deprecated
+  static bool DEFAULT_ENABLE_ENUM = true;
+
+  /**
+   * A predicate indicating whether analysis is to parse and analyze function
+   * bodies.
+   */
+  AnalyzeFunctionBodiesPredicate _analyzeFunctionBodiesPredicate =
+      _analyzeAllFunctionBodies;
+
+  /**
+   * The maximum number of sources for which AST structures should be kept in
+   * the cache.
+   */
+  int cacheSize = DEFAULT_CACHE_SIZE;
+
+  /**
+   * A flag indicating whether analysis is to generate dart2js related hint
+   * results.
+   */
+  bool dart2jsHint = false;
+
+  /**
+   * A flag indicating whether generic methods are to be supported (DEP 22).
+   */
+  bool enableGenericMethods = false;
+
+  /**
+   * A flag indicating whether analysis is to strictly follow the specification
+   * when generating warnings on "call" methods (fixes dartbug.com/21938).
+   */
+  bool enableStrictCallChecks = false;
+
+  /**
+   * A flag indicating whether mixins are allowed to inherit from types other
+   * than Object, and are allowed to reference `super`.
+   */
+  bool enableSuperMixins = false;
+
+  /**
+   * A flag indicating whether errors, warnings and hints should be generated
+   * for sources that are implicitly being analyzed.
+   */
+  bool generateImplicitErrors = true;
+
+  /**
+   * A flag indicating whether errors, warnings and hints should be generated
+   * for sources in the SDK.
+   */
+  bool generateSdkErrors = false;
+
+  /**
+   * A flag indicating whether analysis is to generate hint results (e.g. type
+   * inference based information and pub best practices).
+   */
+  bool hint = true;
+
+  /**
+   * A flag indicating whether incremental analysis should be used.
+   */
+  bool incremental = false;
+
+  /**
+   * A flag indicating whether incremental analysis should be used for API
+   * changes.
+   */
+  bool incrementalApi = false;
+
+  /**
+   * A flag indicating whether validation should be performed after incremental
+   * analysis.
+   */
+  bool incrementalValidation = false;
+
+  /**
+   * A flag indicating whether analysis is to generate lint warnings.
+   */
+  bool lint = false;
+
+  /**
+   * A flag indicating whether analysis is to parse comments.
+   */
+  bool preserveComments = true;
+
+  /**
+   * A flag indicating whether strong-mode analysis should be used.
+   */
+  bool strongMode = false;
+
+  /**
+   * Initialize a newly created set of analysis options to have their default
+   * values.
+   */
+  AnalysisOptionsImpl();
+
+  /**
+   * Initialize a newly created set of analysis options to have the same values
+   * as those in the given set of analysis [options].
+   */
+  @deprecated // Use new AnalysisOptionsImpl.from(options)
+  AnalysisOptionsImpl.con1(AnalysisOptions options) {
+    analyzeFunctionBodiesPredicate = options.analyzeFunctionBodiesPredicate;
+    cacheSize = options.cacheSize;
+    dart2jsHint = options.dart2jsHint;
+    enableStrictCallChecks = options.enableStrictCallChecks;
+    enableSuperMixins = options.enableSuperMixins;
+    generateImplicitErrors = options.generateImplicitErrors;
+    generateSdkErrors = options.generateSdkErrors;
+    hint = options.hint;
+    incremental = options.incremental;
+    incrementalApi = options.incrementalApi;
+    incrementalValidation = options.incrementalValidation;
+    lint = options.lint;
+    preserveComments = options.preserveComments;
+    strongMode = options.strongMode;
+  }
+
+  /**
+   * Initialize a newly created set of analysis options to have the same values
+   * as those in the given set of analysis [options].
+   */
+  AnalysisOptionsImpl.from(AnalysisOptions options) {
+    analyzeFunctionBodiesPredicate = options.analyzeFunctionBodiesPredicate;
+    cacheSize = options.cacheSize;
+    dart2jsHint = options.dart2jsHint;
+    enableStrictCallChecks = options.enableStrictCallChecks;
+    enableSuperMixins = options.enableSuperMixins;
+    generateImplicitErrors = options.generateImplicitErrors;
+    generateSdkErrors = options.generateSdkErrors;
+    hint = options.hint;
+    incremental = options.incremental;
+    incrementalApi = options.incrementalApi;
+    incrementalValidation = options.incrementalValidation;
+    lint = options.lint;
+    preserveComments = options.preserveComments;
+    strongMode = options.strongMode;
+  }
+
+  bool get analyzeFunctionBodies {
+    if (identical(analyzeFunctionBodiesPredicate, _analyzeAllFunctionBodies)) {
+      return true;
+    } else if (identical(
+        analyzeFunctionBodiesPredicate, _analyzeNoFunctionBodies)) {
+      return false;
+    } else {
+      throw new StateError('analyzeFunctionBodiesPredicate in use');
+    }
+  }
+
+  set analyzeFunctionBodies(bool value) {
+    if (value) {
+      analyzeFunctionBodiesPredicate = _analyzeAllFunctionBodies;
+    } else {
+      analyzeFunctionBodiesPredicate = _analyzeNoFunctionBodies;
+    }
+  }
+
+  @override
+  AnalyzeFunctionBodiesPredicate get analyzeFunctionBodiesPredicate =>
+      _analyzeFunctionBodiesPredicate;
+
+  set analyzeFunctionBodiesPredicate(AnalyzeFunctionBodiesPredicate value) {
+    if (value == null) {
+      throw new ArgumentError.notNull('analyzeFunctionBodiesPredicate');
+    }
+    _analyzeFunctionBodiesPredicate = value;
+  }
+
+  @deprecated
+  @override
+  bool get enableAsync => true;
+
+  @deprecated
+  void set enableAsync(bool enable) {
+    // Async support cannot be disabled
+  }
+
+  @deprecated
+  @override
+  bool get enableDeferredLoading => true;
+
+  @deprecated
+  void set enableDeferredLoading(bool enable) {
+    // Deferred loading support cannot be disabled
+  }
+
+  @deprecated
+  @override
+  bool get enableEnum => true;
+
+  @deprecated
+  void set enableEnum(bool enable) {
+    // Enum support cannot be disabled
+  }
+
+  @deprecated
+  @override
+  bool get enableNullAwareOperators => true;
+
+  @deprecated
+  void set enableNullAwareOperators(bool enable) {
+    // Null-aware operator support cannot be disabled
+  }
+
+  /**
+   * Predicate used for [analyzeFunctionBodiesPredicate] when
+   * [analyzeFunctionBodies] is set to `true`.
+   */
+  static bool _analyzeAllFunctionBodies(Source _) => true;
+
+  /**
+   * Predicate used for [analyzeFunctionBodiesPredicate] when
+   * [analyzeFunctionBodies] is set to `false`.
+   */
+  static bool _analyzeNoFunctionBodies(Source _) => false;
+}
+
+/**
+ *
+ */
+class AnalysisResult {
+  /**
+   * The change notices associated with this result, or `null` if there were no
+   * changes and there is no more work to be done.
+   */
+  final List<ChangeNotice> _notices;
+
+  /**
+   * The number of milliseconds required to determine which task was to be
+   * performed.
+   */
+  final int getTime;
+
+  /**
+   * The name of the class of the task that was performed.
+   */
+  final String taskClassName;
+
+  /**
+   * The number of milliseconds required to perform the task.
+   */
+  final int performTime;
+
+  /**
+   * Initialize a newly created analysis result to have the given values. The
+   * [notices] is the change notices associated with this result. The [getTime]
+   * is the number of milliseconds required to determine which task was to be
+   * performed. The [taskClassName] is the name of the class of the task that
+   * was performed. The [performTime] is the number of milliseconds required to
+   * perform the task.
+   */
+  AnalysisResult(
+      this._notices, this.getTime, this.taskClassName, this.performTime);
+
+  /**
+   * Return the change notices associated with this result, or `null` if there
+   * were no changes and there is no more work to be done.
+   */
+  List<ChangeNotice> get changeNotices => _notices;
+
+  /**
+   * Return `true` if there is more to be performed after the task that was
+   * performed.
+   */
+  bool get hasMoreWork => _notices != null;
+}
+
+/**
+ * An analysis task.
+ */
+abstract class AnalysisTask {
+  /**
+   * The context in which the task is to be performed.
+   */
+  final InternalAnalysisContext context;
+
+  /**
+   * The exception that was thrown while performing this task, or `null` if the
+   * task completed successfully.
+   */
+  CaughtException _thrownException;
+
+  /**
+   * Initialize a newly created task to perform analysis within the given
+   * [context].
+   */
+  AnalysisTask(this.context);
+
+  /**
+   * Return the exception that was thrown while performing this task, or `null`
+   * if the task completed successfully.
+   */
+  CaughtException get exception => _thrownException;
+
+  /**
+   * Return a textual description of this task.
+   */
+  String get taskDescription;
+
+  /**
+   * Use the given [visitor] to visit this task. Throws an [AnalysisException]
+   * if the visitor throws the exception.
+   */
+  accept(AnalysisTaskVisitor visitor);
+
+  /**
+   * Perform this analysis task, protected by an exception handler. Throws an
+   * [AnalysisException] if an exception occurs while performing the task.
+   */
+  void internalPerform();
+
+  /**
+   * Perform this analysis task and use the given [visitor] to visit this task
+   * after it has completed. Throws an [AnalysisException] if the visitor throws
+   * the exception.
+   */
+  Object perform(AnalysisTaskVisitor visitor) {
+    try {
+      _safelyPerform();
+    } on AnalysisException catch (exception, stackTrace) {
+      _thrownException = new CaughtException(exception, stackTrace);
+      AnalysisEngine.instance.logger.logInformation(
+          "Task failed: $taskDescription",
+          new CaughtException(exception, stackTrace));
+    }
+    return PerformanceStatistics.analysisTaskVisitor
+        .makeCurrentWhile(() => accept(visitor));
+  }
+
+  @override
+  String toString() => taskDescription;
+
+  /**
+   * Perform this analysis task, ensuring that all exceptions are wrapped in an
+   * [AnalysisException]. Throws an [AnalysisException] if any exception occurs
+   * while performing the task
+   */
+  void _safelyPerform() {
+    try {
+      String contextName = context.name;
+      if (contextName == null) {
+        contextName = 'unnamed';
+      }
+      AnalysisEngine.instance.instrumentationService
+          .logAnalysisTask(contextName, taskDescription);
+      internalPerform();
+    } on AnalysisException {
+      rethrow;
+    } catch (exception, stackTrace) {
+      throw new AnalysisException(
+          exception.toString(), new CaughtException(exception, stackTrace));
+    }
+  }
+}
+
+/**
+ * An object used to visit tasks. While tasks are not structured in any
+ * interesting way, this class provides the ability to dispatch to an
+ * appropriate method.
+ */
+abstract class AnalysisTaskVisitor<E> {
+  /**
+   * Visit the given [task], returning the result of the visit. This method will
+   * throw an AnalysisException if the visitor throws an exception.
+   */
+  E visitGenerateDartErrorsTask(GenerateDartErrorsTask task);
+
+  /**
+   * Visit the given [task], returning the result of the visit. This method will
+   * throw an AnalysisException if the visitor throws an exception.
+   */
+  E visitGenerateDartHintsTask(GenerateDartHintsTask task);
+
+  /**
+   * Visit the given [task], returning the result of the visit. This method will
+   * throw an AnalysisException if the visitor throws an exception.
+   */
+  E visitGenerateDartLintsTask(GenerateDartLintsTask task);
+
+  /**
+   * Visit the given [task], returning the result of the visit. This method will
+   * throw an AnalysisException if the visitor throws an exception.
+   */
+  E visitGetContentTask(GetContentTask task);
+
+  /**
+   * Visit the given [task], returning the result of the visit. This method will
+   * throw an AnalysisException if the visitor throws an exception.
+   */
+  E visitIncrementalAnalysisTask(
+      IncrementalAnalysisTask incrementalAnalysisTask);
+
+  /**
+   * Visit the given [task], returning the result of the visit. This method will
+   * throw an AnalysisException if the visitor throws an exception.
+   */
+  E visitParseDartTask(ParseDartTask task);
+
+  /**
+   * Visit the given [task], returning the result of the visit. This method will
+   * throw an AnalysisException if the visitor throws an exception.
+   */
+  E visitParseHtmlTask(ParseHtmlTask task);
+
+  /**
+   * Visit the given [task], returning the result of the visit. This method will
+   * throw an AnalysisException if the visitor throws an exception.
+   */
+  E visitResolveDartLibraryCycleTask(ResolveDartLibraryCycleTask task);
+
+  /**
+   * Visit the given [task], returning the result of the visit. This method will
+   * throw an AnalysisException if the visitor throws an exception.
+   */
+  E visitResolveDartLibraryTask(ResolveDartLibraryTask task);
+
+  /**
+   * Visit the given [task], returning the result of the visit. This method will
+   * throw an AnalysisException if the visitor throws an exception.
+   */
+  E visitResolveDartUnitTask(ResolveDartUnitTask task);
+
+  /**
+   * Visit the given [task], returning the result of the visit. This method will
+   * throw an AnalysisException if the visitor throws an exception.
+   */
+  E visitResolveHtmlTask(ResolveHtmlTask task);
+
+  /**
+   * Visit the given [task], returning the result of the visit. This method will
+   * throw an AnalysisException if the visitor throws an exception.
+   */
+  E visitScanDartTask(ScanDartTask task);
+}
+
+/**
+ * A `CachedResult` is a single analysis result that is stored in a
+ * [SourceEntry].
+ */
+class CachedResult<E> {
+  /**
+   * The state of the cached value.
+   */
+  CacheState state;
+
+  /**
+   * The value being cached, or `null` if there is no value (for example, when
+   * the [state] is [CacheState.INVALID].
+   */
+  E value;
+
+  /**
+   * Initialize a newly created result holder to represent the value of data
+   * described by the given [descriptor].
+   */
+  CachedResult(DataDescriptor descriptor) {
+    state = CacheState.INVALID;
+    value = descriptor.defaultValue;
+  }
+}
+
+/**
+ * A single partition in an LRU cache of information related to analysis.
+ */
+abstract class CachePartition {
+  /**
+   * The context that owns this partition. Multiple contexts can reference a
+   * partition, but only one context can own it.
+   */
+  final InternalAnalysisContext context;
+
+  /**
+   * The maximum number of sources for which AST structures should be kept in
+   * the cache.
+   */
+  int _maxCacheSize = 0;
+
+  /**
+   * The policy used to determine which pieces of data to remove from the cache.
+   */
+  final CacheRetentionPolicy _retentionPolicy;
+
+  /**
+   * A table mapping the sources belonging to this partition to the information
+   * known about those sources.
+   */
+  HashMap<Source, SourceEntry> _sourceMap = new HashMap<Source, SourceEntry>();
+
+  /**
+   * A list containing the most recently accessed sources with the most recently
+   * used at the end of the list. When more sources are added than the maximum
+   * allowed then the least recently used source will be removed and will have
+   * it's cached AST structure flushed.
+   */
+  List<Source> _recentlyUsed;
+
+  /**
+   * Initialize a newly created cache to maintain at most [maxCacheSize] AST
+   * structures in the cache. The cache is owned by the give [context], and the
+   * [retentionPolicy] will be used to determine which pieces of data to remove
+   * from the cache.
+   */
+  CachePartition(this.context, this._maxCacheSize, this._retentionPolicy) {
+    _recentlyUsed = new List<Source>();
+  }
+
+  /**
+   * Return the number of entries in this partition that have an AST associated
+   * with them.
+   */
+  int get astSize {
+    int astSize = 0;
+    int count = _recentlyUsed.length;
+    for (int i = 0; i < count; i++) {
+      Source source = _recentlyUsed[i];
+      SourceEntry sourceEntry = _sourceMap[source];
+      if (sourceEntry is DartEntry) {
+        if (sourceEntry.anyParsedCompilationUnit != null) {
+          astSize++;
+        }
+      } else if (sourceEntry is HtmlEntry) {
+        if (sourceEntry.anyParsedUnit != null) {
+          astSize++;
+        }
+      }
+    }
+    return astSize;
+  }
+
+  /**
+   * Return a table mapping the sources known to the context to the information
+   * known about the source.
+   *
+   * <b>Note:</b> This method is only visible for use by [AnalysisCache] and
+   * should not be used for any other purpose.
+   */
+  Map<Source, SourceEntry> get map => _sourceMap;
+
+  /**
+   * Set the maximum size of the cache to the given [size].
+   */
+  void set maxCacheSize(int size) {
+    _maxCacheSize = size;
+    while (_recentlyUsed.length > _maxCacheSize) {
+      if (!_flushAstFromCache()) {
+        break;
+      }
+    }
+  }
+
+  /**
+   * Record that the AST associated with the given source was just read from the
+   * cache.
+   */
+  void accessedAst(Source source) {
+    if (_recentlyUsed.remove(source)) {
+      _recentlyUsed.add(source);
+      return;
+    }
+    while (_recentlyUsed.length >= _maxCacheSize) {
+      if (!_flushAstFromCache()) {
+        break;
+      }
+    }
+    _recentlyUsed.add(source);
+  }
+
+  /**
+   * Return `true` if the given [source] is contained in this partition.
+   */
+  bool contains(Source source);
+
+  /**
+   * Return the entry associated with the given [source].
+   */
+  SourceEntry get(Source source) => _sourceMap[source];
+
+  /**
+   * Return an iterator returning all of the map entries mapping sources to
+   * cache entries.
+   */
+  MapIterator<Source, SourceEntry> iterator() =>
+      new SingleMapIterator<Source, SourceEntry>(_sourceMap);
+
+  /**
+   * Associate the given [entry] with the given [source].
+   */
+  void put(Source source, SourceEntry entry) {
+    entry.fixExceptionState();
+    _sourceMap[source] = entry;
+  }
+
+  /**
+   * Remove all information related to the given [source] from this partition.
+   * Return the entry associated with the source, or `null` if there was cache
+   * entry for the source.
+   */
+  SourceEntry remove(Source source) {
+    _recentlyUsed.remove(source);
+    return _sourceMap.remove(source);
+  }
+
+  /**
+   * Record that the AST associated with the given [source] was just removed
+   * from the cache.
+   */
+  void removedAst(Source source) {
+    _recentlyUsed.remove(source);
+  }
+
+  /**
+   * Return the number of sources that are mapped to cache entries.
+   */
+  int size() => _sourceMap.length;
+
+  /**
+   * Record that the AST associated with the given [source] was just stored to
+   * the cache.
+   */
+  void storedAst(Source source) {
+    if (_recentlyUsed.contains(source)) {
+      return;
+    }
+    while (_recentlyUsed.length >= _maxCacheSize) {
+      if (!_flushAstFromCache()) {
+        break;
+      }
+    }
+    _recentlyUsed.add(source);
+  }
+
+  /**
+   * Attempt to flush one AST structure from the cache. Return `true` if a
+   * structure was flushed.
+   */
+  bool _flushAstFromCache() {
+    Source removedSource = _removeAstToFlush();
+    if (removedSource == null) {
+      return false;
+    }
+    SourceEntry sourceEntry = _sourceMap[removedSource];
+    if (sourceEntry is HtmlEntry) {
+      HtmlEntry htmlEntry = sourceEntry;
+      htmlEntry.flushAstStructures();
+    } else if (sourceEntry is DartEntry) {
+      DartEntry dartEntry = sourceEntry;
+      dartEntry.flushAstStructures();
+    }
+    return true;
+  }
+
+  /**
+   * Remove and return one source from the list of recently used sources whose
+   * AST structure can be flushed from the cache. The source that will be
+   * returned will be the source that has been unreferenced for the longest
+   * period of time but that is not a priority for analysis.
+   */
+  Source _removeAstToFlush() {
+    int sourceToRemove = -1;
+    for (int i = 0; i < _recentlyUsed.length; i++) {
+      Source source = _recentlyUsed[i];
+      RetentionPriority priority =
+          _retentionPolicy.getAstPriority(source, _sourceMap[source]);
+      if (priority == RetentionPriority.LOW) {
+        return _recentlyUsed.removeAt(i);
+      } else if (priority == RetentionPriority.MEDIUM && sourceToRemove < 0) {
+        sourceToRemove = i;
+      }
+    }
+    if (sourceToRemove < 0) {
+      // This happens if the retention policy returns a priority of HIGH for all
+      // of the sources that have been recently used. This is the case, for
+      // example, when the list of priority sources is bigger than the current
+      // cache size.
+      return null;
+    }
+    return _recentlyUsed.removeAt(sourceToRemove);
+  }
+}
+
+/**
+ * An object used to determine how important it is for data to be retained in
+ * the analysis cache.
+ */
+abstract class CacheRetentionPolicy {
+  /**
+   * Return the priority of retaining the AST structure for the given [source].
+   */
+  RetentionPriority getAstPriority(Source source, SourceEntry sourceEntry);
+}
+
+/**
+ * The possible states of cached data.
+ */
+class CacheState extends Enum<CacheState> {
+  /**
+   * The data is not in the cache and the last time an attempt was made to
+   * compute the data an exception occurred, making it pointless to attempt to
+   * compute the data again.
+   *
+   * Valid Transitions:
+   * * [INVALID] if a source was modified that might cause the data to be
+   *   computable
+   */
+  static const CacheState ERROR = const CacheState('ERROR', 0);
+
+  /**
+   * The data is not in the cache because it was flushed from the cache in order
+   * to control memory usage. If the data is recomputed, results do not need to
+   * be reported.
+   *
+   * Valid Transitions:
+   * * [IN_PROCESS] if the data is being recomputed
+   * * [INVALID] if a source was modified that causes the data to need to be
+   *   recomputed
+   */
+  static const CacheState FLUSHED = const CacheState('FLUSHED', 1);
+
+  /**
+   * The data might or might not be in the cache but is in the process of being
+   * recomputed.
+   *
+   * Valid Transitions:
+   * * [ERROR] if an exception occurred while trying to compute the data
+   * * [VALID] if the data was successfully computed and stored in the cache
+   */
+  static const CacheState IN_PROCESS = const CacheState('IN_PROCESS', 2);
+
+  /**
+   * The data is not in the cache and needs to be recomputed so that results can
+   * be reported.
+   *
+   * Valid Transitions:
+   * * [IN_PROCESS] if an attempt is being made to recompute the data
+   */
+  static const CacheState INVALID = const CacheState('INVALID', 3);
+
+  /**
+   * The data is in the cache and up-to-date.
+   *
+   * Valid Transitions:
+   * * [FLUSHED] if the data is removed in order to manage memory usage
+   * * [INVALID] if a source was modified in such a way as to invalidate the
+   *   previous data
+   */
+  static const CacheState VALID = const CacheState('VALID', 4);
+
+  static const List<CacheState> values = const [
+    ERROR,
+    FLUSHED,
+    IN_PROCESS,
+    INVALID,
+    VALID
+  ];
+
+  const CacheState(String name, int ordinal) : super(name, ordinal);
+}
+
+/**
+ * An object that represents a change to the analysis results associated with a
+ * given source.
+ */
+abstract class ChangeNotice implements AnalysisErrorInfo {
+  /**
+   * The parsed, but maybe not resolved Dart AST that changed as a result of
+   * the analysis, or `null` if the AST was not changed.
+   */
+  CompilationUnit get parsedDartUnit;
+
+  /**
+   * The fully resolved Dart AST that changed as a result of the analysis, or
+   * `null` if the AST was not changed.
+   */
+  CompilationUnit get resolvedDartUnit;
+
+  /**
+   * The fully resolved HTML AST that changed as a result of the analysis, or
+   * `null` if the AST was not changed.
+   */
+  @deprecated
+  ht.HtmlUnit get resolvedHtmlUnit;
+
+  /**
+   * Return the source for which the result is being reported.
+   */
+  Source get source;
+}
+
+/**
+ * An implementation of a [ChangeNotice].
+ */
+class ChangeNoticeImpl implements ChangeNotice {
+  /**
+   * An empty list of change notices.
+   */
+  static const List<ChangeNoticeImpl> EMPTY_LIST = const <ChangeNoticeImpl>[];
+
+  /**
+   * The source for which the result is being reported.
+   */
+  final Source source;
+
+  /**
+   * The parsed, but maybe not resolved Dart AST that changed as a result of
+   * the analysis, or `null` if the AST was not changed.
+   */
+  CompilationUnit parsedDartUnit;
+
+  /**
+   * The fully resolved Dart AST that changed as a result of the analysis, or
+   * `null` if the AST was not changed.
+   */
+  CompilationUnit resolvedDartUnit;
+
+  /**
+   * The fully resolved HTML AST that changed as a result of the analysis, or
+   * `null` if the AST was not changed.
+   */
+  @deprecated
+  ht.HtmlUnit resolvedHtmlUnit;
+
+  /**
+   * The errors that changed as a result of the analysis, or `null` if errors
+   * were not changed.
+   */
+  List<AnalysisError> _errors;
+
+  /**
+   * The line information associated with the source, or `null` if errors were
+   * not changed.
+   */
+  LineInfo _lineInfo;
+
+  /**
+   * Initialize a newly created notice associated with the given source.
+   *
+   * @param source the source for which the change is being reported
+   */
+  ChangeNoticeImpl(this.source);
+
+  @override
+  List<AnalysisError> get errors => _errors;
+
+  @override
+  LineInfo get lineInfo => _lineInfo;
+
+  /**
+   * Set the errors that changed as a result of the analysis to the given
+   * [errors] and set the line information to the given [lineInfo].
+   */
+  void setErrors(List<AnalysisError> errors, LineInfo lineInfo) {
+    this._errors = errors;
+    this._lineInfo = lineInfo;
+    if (lineInfo == null) {
+      AnalysisEngine.instance.logger.logInformation("No line info: $source",
+          new CaughtException(new AnalysisException(), null));
+    }
+  }
+
+  @override
+  String toString() => "Changes for ${source.fullName}";
+}
+
+/**
+ * An indication of which sources have been added, changed, removed, or deleted.
+ * In the case of a changed source, there are multiple ways of indicating the
+ * nature of the change.
+ *
+ * No source should be added to the change set more than once, either with the
+ * same or a different kind of change. It does not make sense, for example, for
+ * a source to be both added and removed, and it is redundant for a source to be
+ * marked as changed in its entirety and changed in some specific range.
+ */
+class ChangeSet {
+  /**
+   * A list containing the sources that have been added.
+   */
+  final List<Source> addedSources = new List<Source>();
+
+  /**
+   * A list containing the sources that have been changed.
+   */
+  final List<Source> changedSources = new List<Source>();
+
+  /**
+   * A table mapping the sources whose content has been changed to the current
+   * content of those sources.
+   */
+  HashMap<Source, String> _changedContent = new HashMap<Source, String>();
+
+  /**
+   * A table mapping the sources whose content has been changed within a single
+   * range to the current content of those sources and information about the
+   * affected range.
+   */
+  final HashMap<Source, ChangeSet_ContentChange> changedRanges =
+      new HashMap<Source, ChangeSet_ContentChange>();
+
+  /**
+   * A list containing the sources that have been removed.
+   */
+  final List<Source> removedSources = new List<Source>();
+
+  /**
+   * A list containing the source containers specifying additional sources that
+   * have been removed.
+   */
+  final List<SourceContainer> removedContainers = new List<SourceContainer>();
+
+  /**
+   * A list containing the sources that have been deleted.
+   */
+  final List<Source> deletedSources = new List<Source>();
+
+  /**
+   * Return a table mapping the sources whose content has been changed to the
+   * current content of those sources.
+   */
+  Map<Source, String> get changedContents => _changedContent;
+
+  /**
+   * Return `true` if this change set does not contain any changes.
+   */
+  bool get isEmpty => addedSources.isEmpty &&
+      changedSources.isEmpty &&
+      _changedContent.isEmpty &&
+      changedRanges.isEmpty &&
+      removedSources.isEmpty &&
+      removedContainers.isEmpty &&
+      deletedSources.isEmpty;
+
+  /**
+   * Record that the specified [source] has been added and that its content is
+   * the default contents of the source.
+   */
+  void addedSource(Source source) {
+    addedSources.add(source);
+  }
+
+  /**
+   * Record that the specified [source] has been changed and that its content is
+   * the given [contents].
+   */
+  void changedContent(Source source, String contents) {
+    _changedContent[source] = contents;
+  }
+
+  /**
+   * Record that the specified [source] has been changed and that its content is
+   * the given [contents]. The [offset] is the offset into the current contents.
+   * The [oldLength] is the number of characters in the original contents that
+   * were replaced. The [newLength] is the number of characters in the
+   * replacement text.
+   */
+  void changedRange(Source source, String contents, int offset, int oldLength,
+      int newLength) {
+    changedRanges[source] =
+        new ChangeSet_ContentChange(contents, offset, oldLength, newLength);
+  }
+
+  /**
+   * Record that the specified [source] has been changed. If the content of the
+   * source was previously overridden, this has no effect (the content remains
+   * overridden). To cancel (or change) the override, use [changedContent]
+   * instead.
+   */
+  void changedSource(Source source) {
+    changedSources.add(source);
+  }
+
+  /**
+   * Record that the specified [source] has been deleted.
+   */
+  void deletedSource(Source source) {
+    deletedSources.add(source);
+  }
+
+  /**
+   * Record that the specified source [container] has been removed.
+   */
+  void removedContainer(SourceContainer container) {
+    if (container != null) {
+      removedContainers.add(container);
+    }
+  }
+
+  /**
+   * Record that the specified [source] has been removed.
+   */
+  void removedSource(Source source) {
+    if (source != null) {
+      removedSources.add(source);
+    }
+  }
+
+  @override
+  String toString() {
+    StringBuffer buffer = new StringBuffer();
+    bool needsSeparator =
+        _appendSources(buffer, addedSources, false, "addedSources");
+    needsSeparator = _appendSources(
+        buffer, changedSources, needsSeparator, "changedSources");
+    needsSeparator = _appendSources2(
+        buffer, _changedContent, needsSeparator, "changedContent");
+    needsSeparator =
+        _appendSources2(buffer, changedRanges, needsSeparator, "changedRanges");
+    needsSeparator = _appendSources(
+        buffer, deletedSources, needsSeparator, "deletedSources");
+    needsSeparator = _appendSources(
+        buffer, removedSources, needsSeparator, "removedSources");
+    int count = removedContainers.length;
+    if (count > 0) {
+      if (removedSources.isEmpty) {
+        if (needsSeparator) {
+          buffer.write("; ");
+        }
+        buffer.write("removed: from ");
+        buffer.write(count);
+        buffer.write(" containers");
+      } else {
+        buffer.write(", and more from ");
+        buffer.write(count);
+        buffer.write(" containers");
+      }
+    }
+    return buffer.toString();
+  }
+
+  /**
+   * Append the given [sources] to the given [buffer], prefixed with the given
+   * [label] and a separator if [needsSeparator] is `true`. Return `true` if
+   * future lists of sources will need a separator.
+   */
+  bool _appendSources(StringBuffer buffer, List<Source> sources,
+      bool needsSeparator, String label) {
+    if (sources.isEmpty) {
+      return needsSeparator;
+    }
+    if (needsSeparator) {
+      buffer.write("; ");
+    }
+    buffer.write(label);
+    String prefix = " ";
+    for (Source source in sources) {
+      buffer.write(prefix);
+      buffer.write(source.fullName);
+      prefix = ", ";
+    }
+    return true;
+  }
+
+  /**
+   * Append the given [sources] to the given [builder], prefixed with the given
+   * [label] and a separator if [needsSeparator] is `true`. Return `true` if
+   * future lists of sources will need a separator.
+   */
+  bool _appendSources2(StringBuffer buffer, HashMap<Source, dynamic> sources,
+      bool needsSeparator, String label) {
+    if (sources.isEmpty) {
+      return needsSeparator;
+    }
+    if (needsSeparator) {
+      buffer.write("; ");
+    }
+    buffer.write(label);
+    String prefix = " ";
+    for (Source source in sources.keys.toSet()) {
+      buffer.write(prefix);
+      buffer.write(source.fullName);
+      prefix = ", ";
+    }
+    return true;
+  }
+}
+
+/**
+ * A change to the content of a source.
+ */
+class ChangeSet_ContentChange {
+  /**
+   * The new contents of the source.
+   */
+  final String contents;
+
+  /**
+   * The offset into the current contents.
+   */
+  final int offset;
+
+  /**
+   * The number of characters in the original contents that were replaced
+   */
+  final int oldLength;
+
+  /**
+   * The number of characters in the replacement text.
+   */
+  final int newLength;
+
+  /**
+   * Initialize a newly created change object to represent a change to the
+   * content of a source. The [contents] is the new contents of the source. The
+   * [offse] ist the offset into the current contents. The [oldLength] is the
+   * number of characters in the original contents that were replaced. The
+   * [newLength] is the number of characters in the replacement text.
+   */
+  ChangeSet_ContentChange(
+      this.contents, this.offset, this.oldLength, this.newLength);
+}
+
+/**
+ * [ComputedResult] describes a value computed for a [ResultDescriptor].
+ */
+class ComputedResult<V> {
+  /**
+   * The context in which the value was computed.
+   */
+  final AnalysisContext context;
+
+  /**
+   * The descriptor of the result which was computed.
+   */
+  final ResultDescriptor<V> descriptor;
+
+  /**
+   * The target for which the result was computed.
+   */
+  final AnalysisTarget target;
+
+  /**
+   * The computed value.
+   */
+  final V value;
+
+  ComputedResult(this.context, this.descriptor, this.target, this.value);
+
+  @override
+  String toString() => '$descriptor of $target in $context';
+}
+
+/**
+ * A pair containing a library and a list of the (source, entry) pairs for
+ * compilation units in the library.
+ */
+class CycleBuilder_LibraryPair {
+  /**
+   * The library containing the compilation units.
+   */
+  ResolvableLibrary library;
+
+  /**
+   * The (source, entry) pairs representing the compilation units in the
+   * library.
+   */
+  List<CycleBuilder_SourceEntryPair> entryPairs;
+
+  /**
+   * Initialize a newly created pair from the given [library] and [entryPairs].
+   */
+  CycleBuilder_LibraryPair(this.library, this.entryPairs);
+}
+
+/**
+ * A pair containing a source and the cache entry associated with that source.
+ * They are used to reduce the number of times an entry must be looked up in the
+ * cache.
+ */
+class CycleBuilder_SourceEntryPair {
+  /**
+   * The source associated with the entry.
+   */
+  Source source;
+
+  /**
+   * The entry associated with the source.
+   */
+  DartEntry entry;
+
+  /**
+   * Initialize a newly created pair from the given [source] and [entry].
+   */
+  CycleBuilder_SourceEntryPair(this.source, this.entry);
+}
+
+/**
+ * The information cached by an analysis context about an individual Dart file.
+ */
+class DartEntry extends SourceEntry {
+  /**
+   * The data descriptor representing the element model representing a single
+   * compilation unit. This model is incomplete and should not be used except as
+   * input to another task.
+   */
+  static final DataDescriptor<List<AnalysisError>> BUILT_ELEMENT =
+      new DataDescriptor<List<AnalysisError>>("DartEntry.BUILT_ELEMENT");
+
+  /**
+   * The data descriptor representing the AST structure after the element model
+   * has been built (and declarations are resolved) but before other resolution
+   * has been performed.
+   */
+  static final DataDescriptor<CompilationUnit> BUILT_UNIT =
+      new DataDescriptor<CompilationUnit>("DartEntry.BUILT_UNIT");
+
+  /**
+   * The data descriptor representing the list of libraries that contain this
+   * compilation unit.
+   */
+  static final DataDescriptor<List<Source>> CONTAINING_LIBRARIES =
+      new DataDescriptor<List<Source>>(
+          "DartEntry.CONTAINING_LIBRARIES", Source.EMPTY_LIST);
+
+  /**
+   * The data descriptor representing the library element for the library. This
+   * data is only available for Dart files that are the defining compilation
+   * unit of a library.
+   */
+  static final DataDescriptor<LibraryElement> ELEMENT =
+      new DataDescriptor<LibraryElement>("DartEntry.ELEMENT");
+
+  /**
+   * The data descriptor representing the list of exported libraries. This data
+   * is only available for Dart files that are the defining compilation unit of
+   * a library.
+   */
+  static final DataDescriptor<List<Source>> EXPORTED_LIBRARIES =
+      new DataDescriptor<List<Source>>(
+          "DartEntry.EXPORTED_LIBRARIES", Source.EMPTY_LIST);
+
+  /**
+   * The data descriptor representing the hints resulting from auditing the
+   * source.
+   */
+  static final DataDescriptor<List<AnalysisError>> HINTS =
+      new DataDescriptor<List<AnalysisError>>(
+          "DartEntry.HINTS", AnalysisError.NO_ERRORS);
+
+  /**
+   * The data descriptor representing the list of imported libraries. This data
+   * is only available for Dart files that are the defining compilation unit of
+   * a library.
+   */
+  static final DataDescriptor<List<Source>> IMPORTED_LIBRARIES =
+      new DataDescriptor<List<Source>>(
+          "DartEntry.IMPORTED_LIBRARIES", Source.EMPTY_LIST);
+
+  /**
+   * The data descriptor representing the list of included parts. This data is
+   * only available for Dart files that are the defining compilation unit of a
+   * library.
+   */
+  static final DataDescriptor<List<Source>> INCLUDED_PARTS =
+      new DataDescriptor<List<Source>>(
+          "DartEntry.INCLUDED_PARTS", Source.EMPTY_LIST);
+
+  /**
+   * The data descriptor representing the client flag. This data is only
+   * available for Dart files that are the defining compilation unit of a
+   * library.
+   */
+  static final DataDescriptor<bool> IS_CLIENT =
+      new DataDescriptor<bool>("DartEntry.IS_CLIENT", false);
+
+  /**
+   * The data descriptor representing the launchable flag. This data is only
+   * available for Dart files that are the defining compilation unit of a
+   * library.
+   */
+  static final DataDescriptor<bool> IS_LAUNCHABLE =
+      new DataDescriptor<bool>("DartEntry.IS_LAUNCHABLE", false);
+
+  /**
+   * The data descriptor representing lint warnings resulting from auditing the
+   * source.
+   */
+  static final DataDescriptor<List<AnalysisError>> LINTS =
+      new DataDescriptor<List<AnalysisError>>(
+          "DartEntry.LINTS", AnalysisError.NO_ERRORS);
+
+  /**
+   * The data descriptor representing the errors resulting from parsing the
+   * source.
+   */
+  static final DataDescriptor<List<AnalysisError>> PARSE_ERRORS =
+      new DataDescriptor<List<AnalysisError>>(
+          "DartEntry.PARSE_ERRORS", AnalysisError.NO_ERRORS);
+
+  /**
+   * The data descriptor representing the parsed AST structure.
+   */
+  static final DataDescriptor<CompilationUnit> PARSED_UNIT =
+      new DataDescriptor<CompilationUnit>("DartEntry.PARSED_UNIT");
+
+  /**
+   * The data descriptor representing the public namespace of the library. This
+   * data is only available for Dart files that are the defining compilation
+   * unit of a library.
+   */
+  static final DataDescriptor<Namespace> PUBLIC_NAMESPACE =
+      new DataDescriptor<Namespace>("DartEntry.PUBLIC_NAMESPACE");
+
+  /**
+   * The data descriptor representing the errors resulting from resolving the
+   * source.
+   */
+  static final DataDescriptor<List<AnalysisError>> RESOLUTION_ERRORS =
+      new DataDescriptor<List<AnalysisError>>(
+          "DartEntry.RESOLUTION_ERRORS", AnalysisError.NO_ERRORS);
+
+  /**
+   * The data descriptor representing the resolved AST structure.
+   */
+  static final DataDescriptor<CompilationUnit> RESOLVED_UNIT =
+      new DataDescriptor<CompilationUnit>("DartEntry.RESOLVED_UNIT");
+
+  /**
+   * The data descriptor representing the errors resulting from scanning the
+   * source.
+   */
+  static final DataDescriptor<List<AnalysisError>> SCAN_ERRORS =
+      new DataDescriptor<List<AnalysisError>>(
+          "DartEntry.SCAN_ERRORS", AnalysisError.NO_ERRORS);
+
+  /**
+   * The data descriptor representing the source kind.
+   */
+  static final DataDescriptor<SourceKind> SOURCE_KIND =
+      new DataDescriptor<SourceKind>(
+          "DartEntry.SOURCE_KIND", SourceKind.UNKNOWN);
+
+  /**
+   * The data descriptor representing the token stream.
+   */
+  static final DataDescriptor<Token> TOKEN_STREAM =
+      new DataDescriptor<Token>("DartEntry.TOKEN_STREAM");
+
+  /**
+   * The data descriptor representing the errors resulting from verifying the
+   * source.
+   */
+  static final DataDescriptor<List<AnalysisError>> VERIFICATION_ERRORS =
+      new DataDescriptor<List<AnalysisError>>(
+          "DartEntry.VERIFICATION_ERRORS", AnalysisError.NO_ERRORS);
+
+  /**
+   * The list of libraries that contain this compilation unit. The list will be
+   * empty if there are no known libraries that contain this compilation unit.
+   */
+  List<Source> _containingLibraries = new List<Source>();
+
+  /**
+   * The information known as a result of resolving this compilation unit as
+   * part of the library that contains this unit. This field will never be
+   * `null`.
+   */
+  ResolutionState _resolutionState = new ResolutionState();
+
+  /**
+   * Return all of the errors associated with the compilation unit that are
+   * currently cached.
+   */
+  List<AnalysisError> get allErrors {
+    List<AnalysisError> errors = new List<AnalysisError>();
+    errors.addAll(super.allErrors);
+    errors.addAll(getValue(SCAN_ERRORS));
+    errors.addAll(getValue(PARSE_ERRORS));
+    ResolutionState state = _resolutionState;
+    while (state != null) {
+      errors.addAll(state.getValue(RESOLUTION_ERRORS));
+      errors.addAll(state.getValue(VERIFICATION_ERRORS));
+      errors.addAll(state.getValue(HINTS));
+      errors.addAll(state.getValue(LINTS));
+      state = state._nextState;
+    }
+    if (errors.length == 0) {
+      return AnalysisError.NO_ERRORS;
+    }
+    return errors;
+  }
+
+  /**
+   * Return a valid parsed compilation unit, either an unresolved AST structure
+   * or the result of resolving the AST structure in the context of some
+   * library, or `null` if there is no parsed compilation unit available.
+   */
+  CompilationUnit get anyParsedCompilationUnit {
+    if (getState(PARSED_UNIT) == CacheState.VALID) {
+      return getValue(PARSED_UNIT);
+    }
+    ResolutionState state = _resolutionState;
+    while (state != null) {
+      if (state.getState(BUILT_UNIT) == CacheState.VALID) {
+        return state.getValue(BUILT_UNIT);
+      }
+      state = state._nextState;
+    }
+
+    return anyResolvedCompilationUnit;
+  }
+
+  /**
+   * Return the result of resolving the compilation unit as part of any library,
+   * or `null` if there is no cached resolved compilation unit.
+   */
+  CompilationUnit get anyResolvedCompilationUnit {
+    ResolutionState state = _resolutionState;
+    while (state != null) {
+      if (state.getState(RESOLVED_UNIT) == CacheState.VALID) {
+        return state.getValue(RESOLVED_UNIT);
+      }
+      state = state._nextState;
+    }
+    return null;
+  }
+
+  /**
+   * The libraries that are known to contain this part.
+   */
+  List<Source> get containingLibraries => _containingLibraries;
+
+  /**
+   * Set the list of libraries that contain this compilation unit to contain
+   * only the given [librarySource]. This method should only be invoked on
+   * entries that represent a library.
+   */
+  void set containingLibrary(Source librarySource) {
+    _containingLibraries.clear();
+    _containingLibraries.add(librarySource);
+  }
+
+  @override
+  List<DataDescriptor> get descriptors {
+    List<DataDescriptor> result = super.descriptors;
+    result.addAll(<DataDescriptor>[
+      DartEntry.SOURCE_KIND,
+      DartEntry.CONTAINING_LIBRARIES,
+      DartEntry.PARSE_ERRORS,
+      DartEntry.PARSED_UNIT,
+      DartEntry.SCAN_ERRORS,
+      DartEntry.SOURCE_KIND,
+      DartEntry.TOKEN_STREAM
+    ]);
+    SourceKind kind = getValue(DartEntry.SOURCE_KIND);
+    if (kind == SourceKind.LIBRARY) {
+      result.addAll(<DataDescriptor>[
+        DartEntry.ELEMENT,
+        DartEntry.EXPORTED_LIBRARIES,
+        DartEntry.IMPORTED_LIBRARIES,
+        DartEntry.INCLUDED_PARTS,
+        DartEntry.IS_CLIENT,
+        DartEntry.IS_LAUNCHABLE,
+        DartEntry.PUBLIC_NAMESPACE
+      ]);
+    }
+    return result;
+  }
+
+  /**
+   * Return `true` if this entry has an AST structure that can be resolved, even
+   * if it needs to be copied. Returning `true` implies that the method
+   * [resolvableCompilationUnit] will return a non-`null` result.
+   */
+  bool get hasResolvableCompilationUnit {
+    if (getState(PARSED_UNIT) == CacheState.VALID) {
+      return true;
+    }
+    ResolutionState state = _resolutionState;
+    while (state != null) {
+      if (state.getState(BUILT_UNIT) == CacheState.VALID ||
+          state.getState(RESOLVED_UNIT) == CacheState.VALID) {
+        return true;
+      }
+      state = state._nextState;
+    }
+
+    return false;
+  }
+
+  @override
+  SourceKind get kind => getValue(SOURCE_KIND);
+
+  /**
+   * The library sources containing the receiver's source.
+   */
+  List<Source> get librariesContaining {
+    ResolutionState state = _resolutionState;
+    List<Source> result = new List<Source>();
+    while (state != null) {
+      if (state._librarySource != null) {
+        result.add(state._librarySource);
+      }
+      state = state._nextState;
+    }
+    return result;
+  }
+
+  /**
+   * Get a list of all the library-dependent descriptors for which values may
+   * be stored in this SourceEntry.
+   */
+  List<DataDescriptor> get libraryDescriptors {
+    return <DataDescriptor>[
+      DartEntry.BUILT_ELEMENT,
+      DartEntry.BUILT_UNIT,
+      DartEntry.RESOLUTION_ERRORS,
+      DartEntry.RESOLVED_UNIT,
+      DartEntry.VERIFICATION_ERRORS,
+      DartEntry.HINTS,
+      DartEntry.LINTS
+    ];
+  }
+
+  /**
+   * A compilation unit that has not been accessed by any other client and can
+   * therefore safely be modified by the reconciler, or `null` if the source has
+   * not been parsed.
+   */
+  CompilationUnit get resolvableCompilationUnit {
+    if (getState(PARSED_UNIT) == CacheState.VALID) {
+      CompilationUnit unit = getValue(PARSED_UNIT);
+      setState(PARSED_UNIT, CacheState.FLUSHED);
+      return unit;
+    }
+    ResolutionState state = _resolutionState;
+    while (state != null) {
+      if (state.getState(BUILT_UNIT) == CacheState.VALID) {
+        // TODO(brianwilkerson) We're cloning the structure to remove any
+        // previous resolution data, but I'm not sure that's necessary.
+        return state.getValue(BUILT_UNIT).accept(new AstCloner());
+      }
+      if (state.getState(RESOLVED_UNIT) == CacheState.VALID) {
+        return state.getValue(RESOLVED_UNIT).accept(new AstCloner());
+      }
+      state = state._nextState;
+    }
+    return null;
+  }
+
+  /**
+   * Add the given [librarySource] to the list of libraries that contain this
+   * part. This method should only be invoked on entries that represent a part.
+   */
+  void addContainingLibrary(Source librarySource) {
+    _containingLibraries.add(librarySource);
+  }
+
+  /**
+   * Flush any AST structures being maintained by this entry.
+   */
+  void flushAstStructures() {
+    _flush(TOKEN_STREAM);
+    _flush(PARSED_UNIT);
+    _resolutionState.flushAstStructures();
+  }
+
+  /**
+   * Return the state of the data represented by the given [descriptor] in the
+   * context of the given [librarySource].
+   */
+  CacheState getStateInLibrary(
+      DataDescriptor descriptor, Source librarySource) {
+    if (!_isValidLibraryDescriptor(descriptor)) {
+      throw new ArgumentError("Invalid descriptor: $descriptor");
+    }
+    ResolutionState state = _resolutionState;
+    while (state != null) {
+      if (librarySource == state._librarySource) {
+        return state.getState(descriptor);
+      }
+      state = state._nextState;
+    }
+    return CacheState.INVALID;
+  }
+
+  /**
+   * Return the value of the data represented by the given [descriptor] in the
+   * context of the given [librarySource], or `null` if the data represented by
+   * the descriptor is not in the cache.
+   */
+  Object getValueInLibrary(DataDescriptor descriptor, Source librarySource) {
+    if (!_isValidLibraryDescriptor(descriptor)) {
+      throw new ArgumentError("Invalid descriptor: $descriptor");
+    }
+    ResolutionState state = _resolutionState;
+    while (state != null) {
+      if (librarySource == state._librarySource) {
+        return state.getValue(descriptor);
+      }
+      state = state._nextState;
+    }
+    return descriptor.defaultValue;
+  }
+
+  /**
+   * Return `true` if the data represented by the given [descriptor] is marked
+   * as being invalid. If the descriptor represents library-specific data then
+   * this method will return `true` if the data associated with any library it
+   * marked as invalid.
+   */
+  bool hasInvalidData(DataDescriptor descriptor) {
+    if (_isValidDescriptor(descriptor)) {
+      return getState(descriptor) == CacheState.INVALID;
+    } else if (_isValidLibraryDescriptor(descriptor)) {
+      ResolutionState state = _resolutionState;
+      while (state != null) {
+        if (state.getState(descriptor) == CacheState.INVALID) {
+          return true;
+        }
+        state = state._nextState;
+      }
+    }
+    return false;
+  }
+
+  @override
+  void invalidateAllInformation() {
+    super.invalidateAllInformation();
+    setState(SCAN_ERRORS, CacheState.INVALID);
+    setState(TOKEN_STREAM, CacheState.INVALID);
+    setState(SOURCE_KIND, CacheState.INVALID);
+    setState(PARSE_ERRORS, CacheState.INVALID);
+    setState(PARSED_UNIT, CacheState.INVALID);
+    _discardCachedResolutionInformation(true);
+  }
+
+  /**
+   * Invalidate all of the resolution information associated with the
+   * compilation unit. The flag [invalidateUris] should be `true` if the cached
+   * results of converting URIs to source files should also be invalidated.
+   */
+  void invalidateAllResolutionInformation(bool invalidateUris) {
+    if (getState(PARSED_UNIT) == CacheState.FLUSHED) {
+      ResolutionState state = _resolutionState;
+      while (state != null) {
+        if (state.getState(BUILT_UNIT) == CacheState.VALID) {
+          CompilationUnit unit = state.getValue(BUILT_UNIT);
+          setValue(PARSED_UNIT, unit.accept(new AstCloner()));
+          break;
+        } else if (state.getState(RESOLVED_UNIT) == CacheState.VALID) {
+          CompilationUnit unit = state.getValue(RESOLVED_UNIT);
+          setValue(PARSED_UNIT, unit.accept(new AstCloner()));
+          break;
+        }
+        state = state._nextState;
+      }
+    }
+    _discardCachedResolutionInformation(invalidateUris);
+  }
+
+  /**
+   * Invalidate all of the parse and resolution information associated with
+   * this source.
+   */
+  void invalidateParseInformation() {
+    setState(SOURCE_KIND, CacheState.INVALID);
+    setState(PARSE_ERRORS, CacheState.INVALID);
+    setState(PARSED_UNIT, CacheState.INVALID);
+    _containingLibraries.clear();
+    _discardCachedResolutionInformation(true);
+  }
+
+  /**
+   * Record that an [exception] occurred while attempting to build the element
+   * model for the source represented by this entry in the context of the given
+   * [library]. This will set the state of all resolution-based information as
+   * being in error, but will not change the state of any parse results.
+   */
+  void recordBuildElementErrorInLibrary(
+      Source librarySource, CaughtException exception) {
+    setStateInLibrary(BUILT_ELEMENT, librarySource, CacheState.ERROR);
+    setStateInLibrary(BUILT_UNIT, librarySource, CacheState.ERROR);
+    recordResolutionErrorInLibrary(librarySource, exception);
+  }
+
+  @override
+  void recordContentError(CaughtException exception) {
+    super.recordContentError(exception);
+    recordScanError(exception);
+  }
+
+  /**
+   * Record that an error occurred while attempting to generate hints for the
+   * source represented by this entry. This will set the state of all
+   * verification information as being in error. The [librarySource] is the
+   * source of the library in which hints were being generated. The [exception]
+   * is the exception that shows where the error occurred.
+   */
+  void recordHintErrorInLibrary(
+      Source librarySource, CaughtException exception) {
+    this.exception = exception;
+    ResolutionState state = _getOrCreateResolutionState(librarySource);
+    state.recordHintError();
+  }
+
+  /**
+   * Record that an error occurred while attempting to generate lints for the
+   * source represented by this entry. This will set the state of all
+   * verification information as being in error. The [librarySource] is the
+   * source of the library in which lints were being generated. The [exception]
+   * is the exception that shows where the error occurred.
+   */
+  void recordLintErrorInLibrary(
+      Source librarySource, CaughtException exception) {
+    this.exception = exception;
+    ResolutionState state = _getOrCreateResolutionState(librarySource);
+    state.recordLintError();
+  }
+
+  /**
+   * Record that an [exception] occurred while attempting to scan or parse the
+   * entry represented by this entry. This will set the state of all information,
+   * including any resolution-based information, as being in error.
+   */
+  void recordParseError(CaughtException exception) {
+    setState(SOURCE_KIND, CacheState.ERROR);
+    setState(PARSE_ERRORS, CacheState.ERROR);
+    setState(PARSED_UNIT, CacheState.ERROR);
+    setState(EXPORTED_LIBRARIES, CacheState.ERROR);
+    setState(IMPORTED_LIBRARIES, CacheState.ERROR);
+    setState(INCLUDED_PARTS, CacheState.ERROR);
+    recordResolutionError(exception);
+  }
+
+  /**
+   * Record that an [exception] occurred while attempting to resolve the source
+   * represented by this entry. This will set the state of all resolution-based
+   * information as being in error, but will not change the state of any parse
+   * results.
+   */
+  void recordResolutionError(CaughtException exception) {
+    this.exception = exception;
+    setState(ELEMENT, CacheState.ERROR);
+    setState(IS_CLIENT, CacheState.ERROR);
+    setState(IS_LAUNCHABLE, CacheState.ERROR);
+    setState(PUBLIC_NAMESPACE, CacheState.ERROR);
+    _resolutionState.recordResolutionErrorsInAllLibraries();
+  }
+
+  /**
+   * Record that an error occurred while attempting to resolve the source
+   * represented by this entry. This will set the state of all resolution-based
+   * information as being in error, but will not change the state of any parse
+   * results. The [librarySource] is the source of the library in which
+   * resolution was being performed. The [exception] is the exception that shows
+   * where the error occurred.
+   */
+  void recordResolutionErrorInLibrary(
+      Source librarySource, CaughtException exception) {
+    this.exception = exception;
+    setState(ELEMENT, CacheState.ERROR);
+    setState(IS_CLIENT, CacheState.ERROR);
+    setState(IS_LAUNCHABLE, CacheState.ERROR);
+    setState(PUBLIC_NAMESPACE, CacheState.ERROR);
+    ResolutionState state = _getOrCreateResolutionState(librarySource);
+    state.recordResolutionError();
+  }
+
+  /**
+   * Record that an [exception] occurred while attempting to scan or parse the
+   * entry represented by this entry. This will set the state of all
+   * information, including any resolution-based information, as being in error.
+   */
+  @override
+  void recordScanError(CaughtException exception) {
+    super.recordScanError(exception);
+    setState(SCAN_ERRORS, CacheState.ERROR);
+    setState(TOKEN_STREAM, CacheState.ERROR);
+    recordParseError(exception);
+  }
+
+  /**
+   * Record that an [exception] occurred while attempting to generate errors and
+   * warnings for the source represented by this entry. This will set the state
+   * of all verification information as being in error. The [librarySource] is
+   * the source of the library in which verification was being performed. The
+   * [exception] is the exception that shows where the error occurred.
+   */
+  void recordVerificationErrorInLibrary(
+      Source librarySource, CaughtException exception) {
+    this.exception = exception;
+    ResolutionState state = _getOrCreateResolutionState(librarySource);
+    state.recordVerificationError();
+  }
+
+  /**
+   * Remove the given [library] from the list of libraries that contain this
+   * part. This method should only be invoked on entries that represent a part.
+   */
+  void removeContainingLibrary(Source library) {
+    _containingLibraries.remove(library);
+  }
+
+  /**
+   * Remove any resolution information associated with this compilation unit
+   * being part of the given [library], presumably because it is no longer part
+   * of the library.
+   */
+  void removeResolution(Source library) {
+    if (library != null) {
+      if (library == _resolutionState._librarySource) {
+        if (_resolutionState._nextState == null) {
+          _resolutionState.invalidateAllResolutionInformation();
+        } else {
+          _resolutionState = _resolutionState._nextState;
+        }
+      } else {
+        ResolutionState priorState = _resolutionState;
+        ResolutionState state = _resolutionState._nextState;
+        while (state != null) {
+          if (library == state._librarySource) {
+            priorState._nextState = state._nextState;
+            break;
+          }
+          priorState = state;
+          state = state._nextState;
+        }
+      }
+    }
+  }
+
+  /**
+   * Set the state of the data represented by the given [descriptor] in the
+   * context of the given [library] to the given [state].
+   */
+  void setStateInLibrary(
+      DataDescriptor descriptor, Source library, CacheState state) {
+    if (!_isValidLibraryDescriptor(descriptor)) {
+      throw new ArgumentError("Invalid descriptor: $descriptor");
+    }
+    ResolutionState resolutionState = _getOrCreateResolutionState(library);
+    resolutionState.setState(descriptor, state);
+  }
+
+  /**
+   * Set the value of the data represented by the given [descriptor] in the
+   * context of the given [library] to the given [value], and set the state of
+   * that data to [CacheState.VALID].
+   */
+  void setValueInLibrary(
+      DataDescriptor descriptor, Source library, Object value) {
+    if (!_isValidLibraryDescriptor(descriptor)) {
+      throw new ArgumentError("Invalid descriptor: $descriptor");
+    }
+    ResolutionState state = _getOrCreateResolutionState(library);
+    state.setValue(descriptor, value);
+  }
+
+  /**
+   * Invalidate all of the resolution information associated with the
+   * compilation unit. The flag [invalidateUris] should be `true` if the cached
+   * results of converting URIs to source files should also be invalidated.
+   */
+  void _discardCachedResolutionInformation(bool invalidateUris) {
+    setState(ELEMENT, CacheState.INVALID);
+    setState(IS_CLIENT, CacheState.INVALID);
+    setState(IS_LAUNCHABLE, CacheState.INVALID);
+    setState(PUBLIC_NAMESPACE, CacheState.INVALID);
+    _resolutionState.invalidateAllResolutionInformation();
+    if (invalidateUris) {
+      setState(EXPORTED_LIBRARIES, CacheState.INVALID);
+      setState(IMPORTED_LIBRARIES, CacheState.INVALID);
+      setState(INCLUDED_PARTS, CacheState.INVALID);
+    }
+  }
+
+  /**
+   * Return a resolution state for the specified [library], creating one as
+   * necessary.
+   */
+  ResolutionState _getOrCreateResolutionState(Source library) {
+    ResolutionState state = _resolutionState;
+    if (state._librarySource == null) {
+      state._librarySource = library;
+      return state;
+    }
+    while (state._librarySource != library) {
+      if (state._nextState == null) {
+        ResolutionState newState = new ResolutionState();
+        newState._librarySource = library;
+        state._nextState = newState;
+        return newState;
+      }
+      state = state._nextState;
+    }
+    return state;
+  }
+
+  @override
+  bool _isValidDescriptor(DataDescriptor descriptor) {
+    return descriptor == CONTAINING_LIBRARIES ||
+        descriptor == ELEMENT ||
+        descriptor == EXPORTED_LIBRARIES ||
+        descriptor == IMPORTED_LIBRARIES ||
+        descriptor == INCLUDED_PARTS ||
+        descriptor == IS_CLIENT ||
+        descriptor == IS_LAUNCHABLE ||
+        descriptor == PARSED_UNIT ||
+        descriptor == PARSE_ERRORS ||
+        descriptor == PUBLIC_NAMESPACE ||
+        descriptor == SCAN_ERRORS ||
+        descriptor == SOURCE_KIND ||
+        descriptor == TOKEN_STREAM ||
+        super._isValidDescriptor(descriptor);
+  }
+
+  /**
+   * Return `true` if the [descriptor] is valid for this entry when the data is
+   * relative to a library.
+   */
+  bool _isValidLibraryDescriptor(DataDescriptor descriptor) {
+    return descriptor == BUILT_ELEMENT ||
+        descriptor == BUILT_UNIT ||
+        descriptor == HINTS ||
+        descriptor == LINTS ||
+        descriptor == RESOLUTION_ERRORS ||
+        descriptor == RESOLVED_UNIT ||
+        descriptor == VERIFICATION_ERRORS;
+  }
+
+  @override
+  bool _writeDiffOn(StringBuffer buffer, SourceEntry oldEntry) {
+    bool needsSeparator = super._writeDiffOn(buffer, oldEntry);
+    if (oldEntry is! DartEntry) {
+      if (needsSeparator) {
+        buffer.write("; ");
+      }
+      buffer.write("entry type changed; was ");
+      buffer.write(oldEntry.runtimeType.toString());
+      return true;
+    }
+    needsSeparator = _writeStateDiffOn(buffer, needsSeparator, "tokenStream",
+        DartEntry.TOKEN_STREAM, oldEntry);
+    needsSeparator = _writeStateDiffOn(
+        buffer, needsSeparator, "scanErrors", DartEntry.SCAN_ERRORS, oldEntry);
+    needsSeparator = _writeStateDiffOn(
+        buffer, needsSeparator, "sourceKind", DartEntry.SOURCE_KIND, oldEntry);
+    needsSeparator = _writeStateDiffOn(
+        buffer, needsSeparator, "parsedUnit", DartEntry.PARSED_UNIT, oldEntry);
+    needsSeparator = _writeStateDiffOn(buffer, needsSeparator, "parseErrors",
+        DartEntry.PARSE_ERRORS, oldEntry);
+    needsSeparator = _writeStateDiffOn(buffer, needsSeparator,
+        "importedLibraries", DartEntry.IMPORTED_LIBRARIES, oldEntry);
+    needsSeparator = _writeStateDiffOn(buffer, needsSeparator,
+        "exportedLibraries", DartEntry.EXPORTED_LIBRARIES, oldEntry);
+    needsSeparator = _writeStateDiffOn(buffer, needsSeparator, "includedParts",
+        DartEntry.INCLUDED_PARTS, oldEntry);
+    needsSeparator = _writeStateDiffOn(
+        buffer, needsSeparator, "element", DartEntry.ELEMENT, oldEntry);
+    needsSeparator = _writeStateDiffOn(buffer, needsSeparator,
+        "publicNamespace", DartEntry.PUBLIC_NAMESPACE, oldEntry);
+    needsSeparator = _writeStateDiffOn(
+        buffer, needsSeparator, "clientServer", DartEntry.IS_CLIENT, oldEntry);
+    needsSeparator = _writeStateDiffOn(buffer, needsSeparator, "launchable",
+        DartEntry.IS_LAUNCHABLE, oldEntry);
+    // TODO(brianwilkerson) Add better support for containingLibraries.
+    // It would be nice to be able to report on size-preserving changes.
+    int oldLibraryCount = (oldEntry as DartEntry)._containingLibraries.length;
+    int libraryCount = _containingLibraries.length;
+    if (oldLibraryCount != libraryCount) {
+      if (needsSeparator) {
+        buffer.write("; ");
+      }
+      buffer.write("containingLibraryCount = ");
+      buffer.write(oldLibraryCount);
+      buffer.write(" -> ");
+      buffer.write(libraryCount);
+      needsSeparator = true;
+    }
+    //
+    // Report change to the per-library state.
+    //
+    HashMap<Source, ResolutionState> oldStateMap =
+        new HashMap<Source, ResolutionState>();
+    ResolutionState state = (oldEntry as DartEntry)._resolutionState;
+    while (state != null) {
+      Source librarySource = state._librarySource;
+      if (librarySource != null) {
+        oldStateMap[librarySource] = state;
+      }
+      state = state._nextState;
+    }
+    state = _resolutionState;
+    while (state != null) {
+      Source librarySource = state._librarySource;
+      if (librarySource != null) {
+        ResolutionState oldState = oldStateMap.remove(librarySource);
+        if (oldState == null) {
+          if (needsSeparator) {
+            buffer.write("; ");
+          }
+          buffer.write("added resolution for ");
+          buffer.write(librarySource.fullName);
+          needsSeparator = true;
+        } else {
+          needsSeparator = oldState._writeDiffOn(
+              buffer, needsSeparator, oldEntry as DartEntry);
+        }
+      }
+      state = state._nextState;
+    }
+    for (Source librarySource in oldStateMap.keys.toSet()) {
+      if (needsSeparator) {
+        buffer.write("; ");
+      }
+      buffer.write("removed resolution for ");
+      buffer.write(librarySource.fullName);
+      needsSeparator = true;
+    }
+    return needsSeparator;
+  }
+
+  @override
+  void _writeOn(StringBuffer buffer) {
+    buffer.write("Dart: ");
+    super._writeOn(buffer);
+    _writeStateOn(buffer, "tokenStream", TOKEN_STREAM);
+    _writeStateOn(buffer, "scanErrors", SCAN_ERRORS);
+    _writeStateOn(buffer, "sourceKind", SOURCE_KIND);
+    _writeStateOn(buffer, "parsedUnit", PARSED_UNIT);
+    _writeStateOn(buffer, "parseErrors", PARSE_ERRORS);
+    _writeStateOn(buffer, "exportedLibraries", EXPORTED_LIBRARIES);
+    _writeStateOn(buffer, "importedLibraries", IMPORTED_LIBRARIES);
+    _writeStateOn(buffer, "includedParts", INCLUDED_PARTS);
+    _writeStateOn(buffer, "element", ELEMENT);
+    _writeStateOn(buffer, "publicNamespace", PUBLIC_NAMESPACE);
+    _writeStateOn(buffer, "clientServer", IS_CLIENT);
+    _writeStateOn(buffer, "launchable", IS_LAUNCHABLE);
+    _resolutionState._writeOn(buffer);
+  }
+}
+
+/**
+ * An immutable constant representing data that can be stored in the cache.
+ */
+class DataDescriptor<E> {
+  /**
+   * The next artificial hash code.
+   */
+  static int _NEXT_HASH_CODE = 0;
+
+  /**
+   * The artifitial hash code for this object.
+   */
+  final int _hashCode = _NEXT_HASH_CODE++;
+
+  /**
+   * The name of the descriptor, used for debugging purposes.
+   */
+  final String _name;
+
+  /**
+   * The default value used when the data does not exist.
+   */
+  final E defaultValue;
+
+  /**
+   * Initialize a newly created descriptor to have the given [name] and
+   * [defaultValue].
+   */
+  DataDescriptor(this._name, [this.defaultValue = null]);
+
+  @override
+  int get hashCode => _hashCode;
+
+  @override
+  String toString() => _name;
+}
+
+/**
+ * A retention policy that will keep AST's in the cache if there is analysis
+ * information that needs to be computed for a source, where the computation is
+ * dependent on having the AST.
+ */
+class DefaultRetentionPolicy implements CacheRetentionPolicy {
+  /**
+   * An instance of this class that can be shared.
+   */
+  static DefaultRetentionPolicy POLICY = new DefaultRetentionPolicy();
+
+  /**
+   * Return `true` if there is analysis information in the given [dartEntry]
+   * that needs to be computed, where the computation is dependent on having the
+   * AST.
+   */
+  bool astIsNeeded(DartEntry dartEntry) =>
+      dartEntry.hasInvalidData(DartEntry.HINTS) ||
+          dartEntry.hasInvalidData(DartEntry.LINTS) ||
+          dartEntry.hasInvalidData(DartEntry.VERIFICATION_ERRORS) ||
+          dartEntry.hasInvalidData(DartEntry.RESOLUTION_ERRORS);
+
+  @override
+  RetentionPriority getAstPriority(Source source, SourceEntry sourceEntry) {
+    if (sourceEntry is DartEntry) {
+      DartEntry dartEntry = sourceEntry;
+      if (astIsNeeded(dartEntry)) {
+        return RetentionPriority.MEDIUM;
+      }
+    }
+    return RetentionPriority.LOW;
+  }
+}
+
+/**
+ * Instances of the class `GenerateDartErrorsTask` generate errors and warnings for a single
+ * Dart source.
+ */
+class GenerateDartErrorsTask extends AnalysisTask {
+  /**
+   * The source for which errors and warnings are to be produced.
+   */
+  final Source source;
+
+  /**
+   * The compilation unit used to resolve the dependencies.
+   */
+  final CompilationUnit _unit;
+
+  /**
+   * The element model for the library containing the source.
+   */
+  final LibraryElement libraryElement;
+
+  /**
+   * The errors that were generated for the source.
+   */
+  List<AnalysisError> _errors;
+
+  /**
+   * Initialize a newly created task to perform analysis within the given context.
+   *
+   * @param context the context in which the task is to be performed
+   * @param source the source for which errors and warnings are to be produced
+   * @param unit the compilation unit used to resolve the dependencies
+   * @param libraryElement the element model for the library containing the source
+   */
+  GenerateDartErrorsTask(InternalAnalysisContext context, this.source,
+      this._unit, this.libraryElement)
+      : super(context);
+
+  /**
+   * Return the errors that were generated for the source.
+   *
+   * @return the errors that were generated for the source
+   */
+  List<AnalysisError> get errors => _errors;
+
+  @override
+  String get taskDescription =>
+      "generate errors and warnings for ${source.fullName}";
+
+  @override
+  accept(AnalysisTaskVisitor visitor) =>
+      visitor.visitGenerateDartErrorsTask(this);
+
+  @override
+  void internalPerform() {
+    PerformanceStatistics.errors.makeCurrentWhile(() {
+      RecordingErrorListener errorListener = new RecordingErrorListener();
+      ErrorReporter errorReporter = new ErrorReporter(errorListener, source);
+      TypeProvider typeProvider = context.typeProvider;
+      //
+      // Validate the directives
+      //
+      validateDirectives(context, source, _unit, errorListener);
+      //
+      // Use the ConstantVerifier to verify the use of constants.
+      // This needs to happen before using the ErrorVerifier because some error
+      // codes need the computed constant values.
+      //
+      // TODO(paulberry): as a temporary workaround for issue 21572,
+      // ConstantVerifier is being run right after ConstantValueComputer, so we
+      // don't need to run it here.  Once issue 21572 is fixed, re-enable the
+      // call to ConstantVerifier.
+//      ConstantVerifier constantVerifier = new ConstantVerifier(errorReporter, libraryElement, typeProvider);
+//      _unit.accept(constantVerifier);
+      //
+      // Use the ErrorVerifier to compute the rest of the errors.
+      //
+      ErrorVerifier errorVerifier = new ErrorVerifier(
+          errorReporter,
+          libraryElement,
+          typeProvider,
+          new InheritanceManager(libraryElement),
+          context.analysisOptions.enableSuperMixins);
+      _unit.accept(errorVerifier);
+      _errors = errorListener.getErrorsForSource(source);
+    });
+  }
+
+  /**
+   * Check each directive in the given compilation unit to see if the referenced source exists and
+   * report an error if it does not.
+   *
+   * @param context the context in which the library exists
+   * @param librarySource the source representing the library containing the directives
+   * @param unit the compilation unit containing the directives to be validated
+   * @param errorListener the error listener to which errors should be reported
+   */
+  static void validateDirectives(AnalysisContext context, Source librarySource,
+      CompilationUnit unit, AnalysisErrorListener errorListener) {
+    for (Directive directive in unit.directives) {
+      if (directive is UriBasedDirective) {
+        validateReferencedSource(
+            context, librarySource, directive, errorListener);
+      }
+    }
+  }
+
+  /**
+   * Check the given directive to see if the referenced source exists and report an error if it does
+   * not.
+   *
+   * @param context the context in which the library exists
+   * @param librarySource the source representing the library containing the directive
+   * @param directive the directive to be verified
+   * @param errorListener the error listener to which errors should be reported
+   */
+  static void validateReferencedSource(
+      AnalysisContext context,
+      Source librarySource,
+      UriBasedDirective directive,
+      AnalysisErrorListener errorListener) {
+    Source source = directive.source;
+    if (source != null) {
+      if (context.exists(source)) {
+        return;
+      }
+    } else {
+      // Don't report errors already reported by ParseDartTask.resolveDirective
+      if (directive.validate() != null) {
+        return;
+      }
+    }
+    StringLiteral uriLiteral = directive.uri;
+    errorListener.onError(new AnalysisError(
+        librarySource,
+        uriLiteral.offset,
+        uriLiteral.length,
+        CompileTimeErrorCode.URI_DOES_NOT_EXIST,
+        [directive.uriContent]));
+  }
+}
+
+/**
+ * Instances of the class `GenerateDartHintsTask` generate hints for a single Dart library.
+ */
+class GenerateDartHintsTask extends AnalysisTask {
+  /**
+   * The compilation units that comprise the library, with the defining compilation unit appearing
+   * first in the list.
+   */
+  final List<TimestampedData<CompilationUnit>> _units;
+
+  /**
+   * The element model for the library being analyzed.
+   */
+  final LibraryElement libraryElement;
+
+  /**
+   * A table mapping the sources that were analyzed to the hints that were
+   * generated for the sources.
+   */
+  HashMap<Source, List<AnalysisError>> _hintMap;
+
+  /**
+   * Initialize a newly created task to perform analysis within the given context.
+   *
+   * @param context the context in which the task is to be performed
+   * @param units the compilation units that comprise the library, with the defining compilation
+   *          unit appearing first in the list
+   * @param libraryElement the element model for the library being analyzed
+   */
+  GenerateDartHintsTask(
+      InternalAnalysisContext context, this._units, this.libraryElement)
+      : super(context);
+
+  /**
+   * Return a table mapping the sources that were analyzed to the hints that were generated for the
+   * sources, or `null` if the task has not been performed or if the analysis did not complete
+   * normally.
+   *
+   * @return a table mapping the sources that were analyzed to the hints that were generated for the
+   *         sources
+   */
+  HashMap<Source, List<AnalysisError>> get hintMap => _hintMap;
+
+  @override
+  String get taskDescription {
+    Source librarySource = libraryElement.source;
+    if (librarySource == null) {
+      return "generate Dart hints for library without source";
+    }
+    return "generate Dart hints for ${librarySource.fullName}";
+  }
+
+  @override
+  accept(AnalysisTaskVisitor visitor) =>
+      visitor.visitGenerateDartHintsTask(this);
+
+  @override
+  void internalPerform() {
+    //
+    // Gather the compilation units.
+    //
+    int unitCount = _units.length;
+    List<CompilationUnit> compilationUnits =
+        new List<CompilationUnit>(unitCount);
+    for (int i = 0; i < unitCount; i++) {
+      compilationUnits[i] = _units[i].data;
+    }
+    //
+    // Analyze all of the units.
+    //
+    RecordingErrorListener errorListener = new RecordingErrorListener();
+    HintGenerator hintGenerator =
+        new HintGenerator(compilationUnits, context, errorListener);
+    hintGenerator.generateForLibrary();
+    //
+    // Store the results.
+    //
+    _hintMap = new HashMap<Source, List<AnalysisError>>();
+    for (int i = 0; i < unitCount; i++) {
+      Source source = _units[i].data.element.source;
+      _hintMap[source] = errorListener.getErrorsForSource(source);
+    }
+  }
+}
+
+/// Generates lint feedback for a single Dart library.
+class GenerateDartLintsTask extends AnalysisTask {
+  ///The compilation units that comprise the library, with the defining
+  ///compilation unit appearing first in the list.
+  final List<TimestampedData<CompilationUnit>> _units;
+
+  /// The element model for the library being analyzed.
+  final LibraryElement libraryElement;
+
+  /// A mapping of analyzed sources to their associated lint warnings.
+  /// May be [null] if the task has not been performed or if analysis did not
+  /// complete normally.
+  HashMap<Source, List<AnalysisError>> lintMap;
+
+  /// Initialize a newly created task to perform lint checking over these
+  /// [_units] belonging to this [libraryElement] within the given [context].
+  GenerateDartLintsTask(context, this._units, this.libraryElement)
+      : super(context);
+
+  @override
+  String get taskDescription {
+    Source librarySource = libraryElement.source;
+    return (librarySource == null)
+        ? "generate Dart lints for library without source"
+        : "generate Dart lints for ${librarySource.fullName}";
+  }
+
+  @override
+  accept(AnalysisTaskVisitor visitor) =>
+      visitor.visitGenerateDartLintsTask(this);
+
+  @override
+  void internalPerform() {
+    Iterable<CompilationUnit> compilationUnits =
+        _units.map((TimestampedData<CompilationUnit> unit) => unit.data);
+    RecordingErrorListener errorListener = new RecordingErrorListener();
+    LintGenerator lintGenerator =
+        new LintGenerator(compilationUnits, errorListener);
+    lintGenerator.generate();
+
+    lintMap = new HashMap<Source, List<AnalysisError>>();
+    compilationUnits.forEach((CompilationUnit unit) {
+      Source source = unit.element.source;
+      lintMap[source] = errorListener.getErrorsForSource(source);
+    });
+  }
+}
+
+/**
+ * Instances of the class `GetContentTask` get the contents of a source.
+ */
+class GetContentTask extends AnalysisTask {
+  /**
+   * The source to be read.
+   */
+  final Source source;
+
+  /**
+   * A flag indicating whether this task is complete.
+   */
+  bool _complete = false;
+
+  /**
+   * The contents of the source.
+   */
+  String _content;
+
+  /**
+   * The errors that were produced by getting the source content.
+   */
+  final List<AnalysisError> errors = <AnalysisError>[];
+
+  /**
+   * The time at which the contents of the source were last modified.
+   */
+  int _modificationTime = -1;
+
+  /**
+   * Initialize a newly created task to perform analysis within the given context.
+   *
+   * @param context the context in which the task is to be performed
+   * @param source the source to be parsed
+   * @param contentData the time-stamped contents of the source
+   */
+  GetContentTask(InternalAnalysisContext context, this.source)
+      : super(context) {
+    if (source == null) {
+      throw new IllegalArgumentException("Cannot get contents of null source");
+    }
+  }
+
+  /**
+   * Return the contents of the source, or `null` if the task has not completed or if there
+   * was an exception while getting the contents.
+   *
+   * @return the contents of the source
+   */
+  String get content => _content;
+
+  /**
+   * Return `true` if this task is complete. Unlike most tasks, this task is allowed to be
+   * visited more than once in order to support asynchronous IO. If the task is not complete when it
+   * is visited synchronously as part of the [AnalysisTask.perform]
+   * method, it will be visited again, using the same visitor, when the IO operation has been
+   * performed.
+   *
+   * @return `true` if this task is complete
+   */
+  bool get isComplete => _complete;
+
+  /**
+   * Return the time at which the contents of the source that was parsed were last modified, or a
+   * negative value if the task has not yet been performed or if an exception occurred.
+   *
+   * @return the time at which the contents of the source that was parsed were last modified
+   */
+  int get modificationTime => _modificationTime;
+
+  @override
+  String get taskDescription => "get contents of ${source.fullName}";
+
+  @override
+  accept(AnalysisTaskVisitor visitor) => visitor.visitGetContentTask(this);
+
+  @override
+  void internalPerform() {
+    _complete = true;
+    try {
+      TimestampedData<String> data = context.getContents(source);
+      _content = data.data;
+      _modificationTime = data.modificationTime;
+      AnalysisEngine.instance.instrumentationService
+          .logFileRead(source.fullName, _modificationTime, _content);
+    } catch (exception, stackTrace) {
+      errors.add(new AnalysisError(
+          source, 0, 0, ScannerErrorCode.UNABLE_GET_CONTENT, [exception]));
+      throw new AnalysisException("Could not get contents of $source",
+          new CaughtException(exception, stackTrace));
+    }
+  }
+}
+
+/**
+ * The information cached by an analysis context about an individual HTML file.
+ */
+class HtmlEntry extends SourceEntry {
+  /**
+   * The data descriptor representing the HTML element.
+   */
+  static final DataDescriptor<HtmlElement> ELEMENT =
+      new DataDescriptor<HtmlElement>("HtmlEntry.ELEMENT");
+
+  /**
+   * The data descriptor representing the hints resulting from auditing the
+   * source.
+   */
+  static final DataDescriptor<List<AnalysisError>> HINTS =
+      new DataDescriptor<List<AnalysisError>>(
+          "HtmlEntry.HINTS", AnalysisError.NO_ERRORS);
+
+  /**
+   * The data descriptor representing the errors resulting from parsing the
+   * source.
+   */
+  static final DataDescriptor<List<AnalysisError>> PARSE_ERRORS =
+      new DataDescriptor<List<AnalysisError>>(
+          "HtmlEntry.PARSE_ERRORS", AnalysisError.NO_ERRORS);
+
+  /**
+   * The data descriptor representing the parsed AST structure.
+   */
+  static final DataDescriptor<ht.HtmlUnit> PARSED_UNIT =
+      new DataDescriptor<ht.HtmlUnit>("HtmlEntry.PARSED_UNIT");
+
+  /**
+   * The data descriptor representing the resolved AST structure.
+   */
+  static final DataDescriptor<ht.HtmlUnit> RESOLVED_UNIT =
+      new DataDescriptor<ht.HtmlUnit>("HtmlEntry.RESOLVED_UNIT");
+
+  /**
+   * The data descriptor representing the list of referenced libraries.
+   */
+  static final DataDescriptor<List<Source>> REFERENCED_LIBRARIES =
+      new DataDescriptor<List<Source>>(
+          "HtmlEntry.REFERENCED_LIBRARIES", Source.EMPTY_LIST);
+
+  /**
+   * The data descriptor representing the errors resulting from resolving the
+   * source.
+   */
+  static final DataDescriptor<List<AnalysisError>> RESOLUTION_ERRORS =
+      new DataDescriptor<List<AnalysisError>>(
+          "HtmlEntry.RESOLUTION_ERRORS", AnalysisError.NO_ERRORS);
+
+  /**
+   * Return all of the errors associated with the HTML file that are currently
+   * cached.
+   */
+  List<AnalysisError> get allErrors {
+    List<AnalysisError> errors = new List<AnalysisError>();
+    errors.addAll(super.allErrors);
+    errors.addAll(getValue(PARSE_ERRORS));
+    errors.addAll(getValue(RESOLUTION_ERRORS));
+    errors.addAll(getValue(HINTS));
+    if (errors.length == 0) {
+      return AnalysisError.NO_ERRORS;
+    }
+    return errors;
+  }
+
+  /**
+   * Return a valid parsed unit, either an unresolved AST structure or the
+   * result of resolving the AST structure, or `null` if there is no parsed unit
+   * available.
+   */
+  ht.HtmlUnit get anyParsedUnit {
+    if (getState(PARSED_UNIT) == CacheState.VALID) {
+      return getValue(PARSED_UNIT);
+    }
+    if (getState(RESOLVED_UNIT) == CacheState.VALID) {
+      return getValue(RESOLVED_UNIT);
+    }
+    return null;
+  }
+
+  @override
+  List<DataDescriptor> get descriptors {
+    List<DataDescriptor> result = super.descriptors;
+    result.addAll([
+      HtmlEntry.ELEMENT,
+      HtmlEntry.PARSE_ERRORS,
+      HtmlEntry.PARSED_UNIT,
+      HtmlEntry.RESOLUTION_ERRORS,
+      HtmlEntry.RESOLVED_UNIT,
+      HtmlEntry.HINTS
+    ]);
+    return result;
+  }
+
+  @override
+  SourceKind get kind => SourceKind.HTML;
+
+  /**
+   * Flush any AST structures being maintained by this entry.
+   */
+  void flushAstStructures() {
+    _flush(PARSED_UNIT);
+    _flush(RESOLVED_UNIT);
+  }
+
+  @override
+  void invalidateAllInformation() {
+    super.invalidateAllInformation();
+    setState(PARSE_ERRORS, CacheState.INVALID);
+    setState(PARSED_UNIT, CacheState.INVALID);
+    setState(RESOLVED_UNIT, CacheState.INVALID);
+    invalidateAllResolutionInformation(true);
+  }
+
+  /**
+   * Invalidate all of the resolution information associated with the HTML file.
+   * If [invalidateUris] is `true`, the cached results of converting URIs to
+   * source files should also be invalidated.
+   */
+  void invalidateAllResolutionInformation(bool invalidateUris) {
+    setState(RESOLVED_UNIT, CacheState.INVALID);
+    setState(ELEMENT, CacheState.INVALID);
+    setState(RESOLUTION_ERRORS, CacheState.INVALID);
+    setState(HINTS, CacheState.INVALID);
+    if (invalidateUris) {
+      setState(REFERENCED_LIBRARIES, CacheState.INVALID);
+    }
+  }
+
+  /**
+   * Invalidate all of the parse and resolution information associated with
+   * this source.
+   */
+  void invalidateParseInformation() {
+    setState(PARSE_ERRORS, CacheState.INVALID);
+    setState(PARSED_UNIT, CacheState.INVALID);
+    invalidateAllResolutionInformation(true);
+  }
+
+  @override
+  void recordContentError(CaughtException exception) {
+    super.recordContentError(exception);
+    recordParseError(exception);
+  }
+
+  /**
+   * Record that an [exception] was encountered while attempting to parse the
+   * source associated with this entry.
+   */
+  void recordParseError(CaughtException exception) {
+    // If the scanning and parsing of HTML are separated,
+    // the following line can be removed.
+    recordScanError(exception);
+    setState(PARSE_ERRORS, CacheState.ERROR);
+    setState(PARSED_UNIT, CacheState.ERROR);
+    setState(REFERENCED_LIBRARIES, CacheState.ERROR);
+    recordResolutionError(exception);
+  }
+
+  /**
+   * Record that an [exception] was encountered while attempting to resolve the
+   * source associated with this entry.
+   */
+  void recordResolutionError(CaughtException exception) {
+    this.exception = exception;
+    setState(RESOLVED_UNIT, CacheState.ERROR);
+    setState(ELEMENT, CacheState.ERROR);
+    setState(RESOLUTION_ERRORS, CacheState.ERROR);
+    setState(HINTS, CacheState.ERROR);
+  }
+
+  @override
+  bool _isValidDescriptor(DataDescriptor descriptor) {
+    return descriptor == ELEMENT ||
+        descriptor == HINTS ||
+        descriptor == PARSED_UNIT ||
+        descriptor == PARSE_ERRORS ||
+        descriptor == REFERENCED_LIBRARIES ||
+        descriptor == RESOLUTION_ERRORS ||
+        descriptor == RESOLVED_UNIT ||
+        super._isValidDescriptor(descriptor);
+  }
+
+  @override
+  bool _writeDiffOn(StringBuffer buffer, SourceEntry oldEntry) {
+    bool needsSeparator = super._writeDiffOn(buffer, oldEntry);
+    if (oldEntry is! HtmlEntry) {
+      if (needsSeparator) {
+        buffer.write("; ");
+      }
+      buffer.write("entry type changed; was ");
+      buffer.write(oldEntry.runtimeType);
+      return true;
+    }
+    needsSeparator = _writeStateDiffOn(buffer, needsSeparator, "parseErrors",
+        HtmlEntry.PARSE_ERRORS, oldEntry);
+    needsSeparator = _writeStateDiffOn(
+        buffer, needsSeparator, "parsedUnit", HtmlEntry.PARSED_UNIT, oldEntry);
+    needsSeparator = _writeStateDiffOn(buffer, needsSeparator, "resolvedUnit",
+        HtmlEntry.RESOLVED_UNIT, oldEntry);
+    needsSeparator = _writeStateDiffOn(buffer, needsSeparator,
+        "resolutionErrors", HtmlEntry.RESOLUTION_ERRORS, oldEntry);
+    needsSeparator = _writeStateDiffOn(buffer, needsSeparator,
+        "referencedLibraries", HtmlEntry.REFERENCED_LIBRARIES, oldEntry);
+    needsSeparator = _writeStateDiffOn(
+        buffer, needsSeparator, "element", HtmlEntry.ELEMENT, oldEntry);
+    return needsSeparator;
+  }
+
+  @override
+  void _writeOn(StringBuffer buffer) {
+    buffer.write("Html: ");
+    super._writeOn(buffer);
+    _writeStateOn(buffer, "parseErrors", PARSE_ERRORS);
+    _writeStateOn(buffer, "parsedUnit", PARSED_UNIT);
+    _writeStateOn(buffer, "resolvedUnit", RESOLVED_UNIT);
+    _writeStateOn(buffer, "resolutionErrors", RESOLUTION_ERRORS);
+    _writeStateOn(buffer, "referencedLibraries", REFERENCED_LIBRARIES);
+    _writeStateOn(buffer, "element", ELEMENT);
+  }
+}
+
+/**
+ * An event indicating when a source either starts or stops being implicitly
+ * analyzed.
+ */
+class ImplicitAnalysisEvent {
+  /**
+   * The source whose status has changed.
+   */
+  final Source source;
+
+  /**
+   * A flag indicating whether the source is now being analyzed.
+   */
+  final bool isAnalyzed;
+
+  /**
+   * Initialize a newly created event to indicate that the given [source] has
+   * changed it status to match the [isAnalyzed] flag.
+   */
+  ImplicitAnalysisEvent(this.source, this.isAnalyzed);
+
+  @override
+  String toString() =>
+      '${isAnalyzed ? '' : 'not '}analyzing ${source.fullName}';
+}
+
+/**
+ * Instances of the class `IncrementalAnalysisCache` hold information used to perform
+ * incremental analysis.
+ *
+ * See [AnalysisContextImpl.setChangedContents].
+ */
+class IncrementalAnalysisCache {
+  final Source librarySource;
+
+  final Source source;
+
+  final String oldContents;
+
+  final CompilationUnit resolvedUnit;
+
+  String _newContents;
+
+  int _offset = 0;
+
+  int _oldLength = 0;
+
+  int _newLength = 0;
+
+  IncrementalAnalysisCache(
+      this.librarySource,
+      this.source,
+      this.resolvedUnit,
+      this.oldContents,
+      this._newContents,
+      this._offset,
+      this._oldLength,
+      this._newLength);
+
+  /**
+   * Determine if the cache contains source changes that need to be analyzed
+   *
+   * @return `true` if the cache contains changes to be analyzed, else `false`
+   */
+  bool get hasWork => _oldLength > 0 || _newLength > 0;
+
+  /**
+   * Return the current contents for the receiver's source.
+   *
+   * @return the contents (not `null`)
+   */
+  String get newContents => _newContents;
+
+  /**
+   * Return the number of characters in the replacement text.
+   *
+   * @return the replacement length (zero or greater)
+   */
+  int get newLength => _newLength;
+
+  /**
+   * Return the character position of the first changed character.
+   *
+   * @return the offset (zero or greater)
+   */
+  int get offset => _offset;
+
+  /**
+   * Return the number of characters that were replaced.
+   *
+   * @return the replaced length (zero or greater)
+   */
+  int get oldLength => _oldLength;
+
+  /**
+   * Determine if the incremental analysis result can be cached for the next incremental analysis.
+   *
+   * @param cache the prior incremental analysis cache
+   * @param unit the incrementally updated compilation unit
+   * @return the cache used for incremental analysis or `null` if incremental analysis results
+   *         cannot be cached for the next incremental analysis
+   */
+  static IncrementalAnalysisCache cacheResult(
+      IncrementalAnalysisCache cache, CompilationUnit unit) {
+    if (cache != null && unit != null) {
+      return new IncrementalAnalysisCache(cache.librarySource, cache.source,
+          unit, cache._newContents, cache._newContents, 0, 0, 0);
+    }
+    return null;
+  }
+
+  /**
+   * Determine if the cache should be cleared.
+   *
+   * @param cache the prior cache or `null` if none
+   * @param source the source being updated (not `null`)
+   * @return the cache used for incremental analysis or `null` if incremental analysis cannot
+   *         be performed
+   */
+  static IncrementalAnalysisCache clear(
+      IncrementalAnalysisCache cache, Source source) {
+    if (cache == null || cache.source == source) {
+      return null;
+    }
+    return cache;
+  }
+
+  /**
+   * Determine if incremental analysis can be performed from the given information.
+   *
+   * @param cache the prior cache or `null` if none
+   * @param source the source being updated (not `null`)
+   * @param oldContents the original source contents prior to this update (may be `null`)
+   * @param newContents the new contents after this incremental change (not `null`)
+   * @param offset the offset at which the change occurred
+   * @param oldLength the length of the text being replaced
+   * @param newLength the length of the replacement text
+   * @param sourceEntry the cached entry for the given source or `null` if none
+   * @return the cache used for incremental analysis or `null` if incremental analysis cannot
+   *         be performed
+   */
+  static IncrementalAnalysisCache update(
+      IncrementalAnalysisCache cache,
+      Source source,
+      String oldContents,
+      String newContents,
+      int offset,
+      int oldLength,
+      int newLength,
+      SourceEntry sourceEntry) {
+    // Determine the cache resolved unit
+    Source librarySource = null;
+    CompilationUnit unit = null;
+    if (sourceEntry is DartEntry) {
+      DartEntry dartEntry = sourceEntry;
+      List<Source> librarySources = dartEntry.librariesContaining;
+      if (librarySources.length == 1) {
+        librarySource = librarySources[0];
+        if (librarySource != null) {
+          unit = dartEntry.getValueInLibrary(
+              DartEntry.RESOLVED_UNIT, librarySource);
+        }
+      }
+    }
+    // Create a new cache if there is not an existing cache or the source is
+    // different or a new resolved compilation unit is available.
+    if (cache == null || cache.source != source || unit != null) {
+      if (unit == null) {
+        return null;
+      }
+      if (oldContents == null) {
+        if (oldLength != 0) {
+          return null;
+        }
+        oldContents =
+            "${newContents.substring(0, offset)}${newContents.substring(offset + newLength)}";
+      }
+      return new IncrementalAnalysisCache(librarySource, source, unit,
+          oldContents, newContents, offset, oldLength, newLength);
+    }
+    // Update the existing cache if the change is contiguous
+    if (cache._oldLength == 0 && cache._newLength == 0) {
+      cache._offset = offset;
+      cache._oldLength = oldLength;
+      cache._newLength = newLength;
+    } else {
+      if (cache._offset > offset || offset > cache._offset + cache._newLength) {
+        return null;
+      }
+      cache._newLength += newLength - oldLength;
+    }
+    cache._newContents = newContents;
+    return cache;
+  }
+
+  /**
+   * Verify that the incrementally parsed and resolved unit in the incremental cache is structurally
+   * equivalent to the fully parsed unit.
+   *
+   * @param cache the prior cache or `null` if none
+   * @param source the source of the compilation unit that was parsed (not `null`)
+   * @param unit the compilation unit that was just parsed
+   * @return the cache used for incremental analysis or `null` if incremental analysis results
+   *         cannot be cached for the next incremental analysis
+   */
+  static IncrementalAnalysisCache verifyStructure(
+      IncrementalAnalysisCache cache, Source source, CompilationUnit unit) {
+    if (cache != null && unit != null && cache.source == source) {
+      if (!AstComparator.equalNodes(cache.resolvedUnit, unit)) {
+        return null;
+      }
+    }
+    return cache;
+  }
+}
+
+/**
+ * Instances of the class `IncrementalAnalysisTask` incrementally update existing analysis.
+ */
+class IncrementalAnalysisTask extends AnalysisTask {
+  /**
+   * The information used to perform incremental analysis.
+   */
+  final IncrementalAnalysisCache cache;
+
+  /**
+   * The compilation unit that was produced by incrementally updating the existing unit.
+   */
+  CompilationUnit _updatedUnit;
+
+  /**
+   * Initialize a newly created task to perform analysis within the given context.
+   *
+   * @param context the context in which the task is to be performed
+   * @param cache the incremental analysis cache used to perform the analysis
+   */
+  IncrementalAnalysisTask(InternalAnalysisContext context, this.cache)
+      : super(context);
+
+  /**
+   * Return the compilation unit that was produced by incrementally updating the existing
+   * compilation unit, or `null` if the task has not yet been performed, could not be
+   * performed, or if an exception occurred.
+   *
+   * @return the compilation unit
+   */
+  CompilationUnit get compilationUnit => _updatedUnit;
+
+  /**
+   * Return the source that is to be incrementally analyzed.
+   *
+   * @return the source
+   */
+  Source get source => cache != null ? cache.source : null;
+
+  @override
+  String get taskDescription =>
+      "incremental analysis ${cache != null ? cache.source : "null"}";
+
+  /**
+   * Return the type provider used for incremental resolution.
+   *
+   * @return the type provider (or `null` if an exception occurs)
+   */
+  TypeProvider get typeProvider {
+    try {
+      return context.typeProvider;
+    } on AnalysisException {
+      return null;
+    }
+  }
+
+  @override
+  accept(AnalysisTaskVisitor visitor) =>
+      visitor.visitIncrementalAnalysisTask(this);
+
+  @override
+  void internalPerform() {
+    if (cache == null) {
+      return;
+    }
+    // Only handle small changes
+    if (cache.oldLength > 0 || cache.newLength > 30) {
+      return;
+    }
+    // Produce an updated token stream
+    CharacterReader reader = new CharSequenceReader(cache.newContents);
+    BooleanErrorListener errorListener = new BooleanErrorListener();
+    IncrementalScanner scanner = new IncrementalScanner(
+        cache.source, reader, errorListener, context.analysisOptions);
+    scanner.rescan(cache.resolvedUnit.beginToken, cache.offset, cache.oldLength,
+        cache.newLength);
+    if (errorListener.errorReported) {
+      return;
+    }
+    // Produce an updated AST
+    IncrementalParser parser = new IncrementalParser(
+        cache.source, scanner.tokenMap, AnalysisErrorListener.NULL_LISTENER);
+    _updatedUnit = parser.reparse(cache.resolvedUnit, scanner.leftToken,
+        scanner.rightToken, cache.offset, cache.offset + cache.oldLength);
+    // Update the resolution
+    TypeProvider typeProvider = this.typeProvider;
+    if (_updatedUnit != null && typeProvider != null) {
+      CompilationUnitElement element = _updatedUnit.element;
+      if (element != null) {
+        LibraryElement library = element.library;
+        if (library != null) {
+          IncrementalResolver resolver = new IncrementalResolver(null, null,
+              null, element, cache.offset, cache.oldLength, cache.newLength);
+          resolver.resolve(parser.updatedNode);
+        }
+      }
+    }
+  }
+}
+
+/**
+ * Additional behavior for an analysis context that is required by internal
+ * users of the context.
+ */
+abstract class InternalAnalysisContext implements AnalysisContext {
+  /**
+   * A table mapping the sources known to the context to the information known
+   * about the source.
+   *
+   * TODO(scheglov) add the type, once we have only one cache.
+   */
+  dynamic get analysisCache;
+
+  /**
+   * Allow the client to supply its own content cache.  This will take the
+   * place of the content cache created by default, allowing clients to share
+   * the content cache between contexts.
+   */
+  set contentCache(ContentCache value);
+
+  /**
+   * Return a list of the explicit targets being analyzed by this context.
+   */
+  List<AnalysisTarget> get explicitTargets;
+
+  /**
+   * A factory to override how [LibraryResolver] is created.
+   */
+  LibraryResolverFactory get libraryResolverFactory;
+
+  /**
+   * Return a list containing all of the sources that have been marked as
+   * priority sources. Clients must not modify the returned list.
+   */
+  List<Source> get prioritySources;
+
+  /**
+   * Return a list of the priority targets being analyzed by this context.
+   */
+  List<AnalysisTarget> get priorityTargets;
+
+  /**
+   * The partition that contains analysis results that are not shared with other
+   * contexts.
+   *
+   * TODO(scheglov) add the type, once we have only one cache.
+   */
+  dynamic get privateAnalysisCachePartition;
+
+  /**
+   * A factory to override how [ResolverVisitor] is created.
+   */
+  ResolverVisitorFactory get resolverVisitorFactory;
+
+  /**
+   * Returns a statistics about this context.
+   */
+  AnalysisContextStatistics get statistics;
+
+  /**
+   * Sets the [TypeProvider] for this context.
+   */
+  void set typeProvider(TypeProvider typeProvider);
+
+  /**
+   * A factory to override how [TypeResolverVisitor] is created.
+   */
+  TypeResolverVisitorFactory get typeResolverVisitorFactory;
+
+  /**
+   * Return a list containing the sources of the libraries that are exported by
+   * the library with the given [source]. The list will be empty if the given
+   * source is invalid, if the given source does not represent a library, or if
+   * the library does not export any other libraries.
+   *
+   * Throws an [AnalysisException] if the exported libraries could not be
+   * computed.
+   */
+  List<Source> computeExportedLibraries(Source source);
+
+  /**
+   * Return a list containing the sources of the libraries that are imported by
+   * the library with the given [source]. The list will be empty if the given
+   * source is invalid, if the given source does not represent a library, or if
+   * the library does not import any other libraries.
+   *
+   * Throws an [AnalysisException] if the imported libraries could not be
+   * computed.
+   */
+  List<Source> computeImportedLibraries(Source source);
+
+  /**
+   * Return an AST structure corresponding to the given [source], but ensure
+   * that the structure has not already been resolved and will not be resolved
+   * by any other threads or in any other library.
+   *
+   * Throws an [AnalysisException] if the analysis could not be performed.
+   *
+   * <b>Note:</b> This method cannot be used in an async environment
+   */
+  CompilationUnit computeResolvableCompilationUnit(Source source);
+
+  /**
+   * Return all the resolved [CompilationUnit]s for the given [source] if not
+   * flushed, otherwise return `null` and ensures that the [CompilationUnit]s
+   * will be eventually returned to the client from [performAnalysisTask].
+   */
+  List<CompilationUnit> ensureResolvedDartUnits(Source source);
+
+  /**
+   * Return the cache entry associated with the given [target].
+   */
+  cache.CacheEntry getCacheEntry(AnalysisTarget target);
+
+  /**
+   * Return context that owns the given [source].
+   */
+  InternalAnalysisContext getContextFor(Source source);
+
+  /**
+   * Return a change notice for the given [source], creating one if one does not
+   * already exist.
+   */
+  ChangeNoticeImpl getNotice(Source source);
+
+  /**
+   * Return a namespace containing mappings for all of the public names defined
+   * by the given [library].
+   */
+  Namespace getPublicNamespace(LibraryElement library);
+
+  /**
+   * Respond to a change which has been made to the given [source] file.
+   * [originalContents] is the former contents of the file, and [newContents]
+   * is the updated contents.  If [notify] is true, a source changed event is
+   * triggered.
+   *
+   * Normally it should not be necessary for clients to call this function,
+   * since it will be automatically invoked in response to a call to
+   * [applyChanges] or [setContents].  However, if this analysis context is
+   * sharing its content cache with other contexts, then the client must
+   * manually update the content cache and call this function for each context.
+   *
+   * Return `true` if the change was significant to this context (i.e. [source]
+   * is either implicitly or explicitly analyzed by this context, and a change
+   * actually occurred).
+   */
+  bool handleContentsChanged(
+      Source source, String originalContents, String newContents, bool notify);
+
+  /**
+   * Given an [elementMap] mapping the source for the libraries represented by
+   * the corresponding elements to the elements representing the libraries,
+   * record those mappings.
+   */
+  void recordLibraryElements(Map<Source, LibraryElement> elementMap);
+
+  /**
+   * Return `true` if errors should be produced for the given [source].
+   * The [entry] associated with the source is passed in for efficiency.
+   *
+   * TODO(scheglov) remove [entry] after migration to the new task model.
+   * It is not used there anyway.
+   */
+  bool shouldErrorsBeAnalyzed(Source source, Object entry);
+
+  /**
+   * For testing only: flush all representations of the AST (both resolved and
+   * unresolved) for the given [source] out of the cache.
+   */
+  void test_flushAstStructures(Source source);
+
+  /**
+   * Call the given callback function for eache cache item in the context.
+   */
+  @deprecated
+  void visitCacheItems(void callback(Source source, SourceEntry dartEntry,
+      DataDescriptor rowDesc, CacheState state));
+
+  /**
+   * Visit all entries of the content cache.
+   */
+  void visitContentCache(ContentCacheVisitor visitor);
+}
+
+/**
+ * An object that can be used to receive information about errors within the
+ * analysis engine. Implementations usually write this information to a file,
+ * but can also record the information for later use (such as during testing) or
+ * even ignore the information.
+ */
+abstract class Logger {
+  /**
+   * A logger that ignores all logging.
+   */
+  static final Logger NULL = new NullLogger();
+
+  /**
+   * Log the given message as an error. The [message] is expected to be an
+   * explanation of why the error occurred or what it means. The [exception] is
+   * expected to be the reason for the error. At least one argument must be
+   * provided.
+   */
+  void logError(String message, [CaughtException exception]);
+
+  /**
+   * Log the given [exception] as one representing an error. The [message] is an
+   * explanation of why the error occurred or what it means.
+   */
+  @deprecated // Use logError(message, exception)
+  void logError2(String message, Object exception);
+
+  /**
+   * Log the given informational message. The [message] is expected to be an
+   * explanation of why the error occurred or what it means. The [exception] is
+   * expected to be the reason for the error.
+   */
+  void logInformation(String message, [CaughtException exception]);
+
+  /**
+   * Log the given [exception] as one representing an informational message. The
+   * [message] is an explanation of why the error occurred or what it means.
+   */
+  @deprecated // Use logInformation(message, exception)
+  void logInformation2(String message, Object exception);
+}
+
+/**
+ * An implementation of [Logger] that does nothing.
+ */
+class NullLogger implements Logger {
+  @override
+  void logError(String message, [CaughtException exception]) {}
+
+  @override
+  void logError2(String message, Object exception) {}
+
+  @override
+  void logInformation(String message, [CaughtException exception]) {}
+
+  @override
+  void logInformation2(String message, Object exception) {}
+}
+
+/**
+ * An exception created when an analysis attempt fails because a source was
+ * deleted between the time the analysis started and the time the results of the
+ * analysis were ready to be recorded.
+ */
+class ObsoleteSourceAnalysisException extends AnalysisException {
+  /**
+   * The source that was removed while it was being analyzed.
+   */
+  Source _source;
+
+  /**
+   * Initialize a newly created exception to represent the removal of the given
+   * [source].
+   */
+  ObsoleteSourceAnalysisException(Source source)
+      : super(
+            "The source '${source.fullName}' was removed while it was being analyzed") {
+    this._source = source;
+  }
+
+  /**
+   * Return the source that was removed while it was being analyzed.
+   */
+  Source get source => _source;
+}
+
+/**
+ * Instances of the class `ParseDartTask` parse a specific source as a Dart file.
+ */
+class ParseDartTask extends AnalysisTask {
+  /**
+   * The source to be parsed.
+   */
+  final Source source;
+
+  /**
+   * The head of the token stream used for parsing.
+   */
+  final Token _tokenStream;
+
+  /**
+   * The line information associated with the source.
+   */
+  final LineInfo lineInfo;
+
+  /**
+   * The compilation unit that was produced by parsing the source.
+   */
+  CompilationUnit _unit;
+
+  /**
+   * A flag indicating whether the source contains a 'part of' directive.
+   */
+  bool _containsPartOfDirective = false;
+
+  /**
+   * A flag indicating whether the source contains any directive other than a 'part of' directive.
+   */
+  bool _containsNonPartOfDirective = false;
+
+  /**
+   * A set containing the sources referenced by 'export' directives.
+   */
+  HashSet<Source> _exportedSources = new HashSet<Source>();
+
+  /**
+   * A set containing the sources referenced by 'import' directives.
+   */
+  HashSet<Source> _importedSources = new HashSet<Source>();
+
+  /**
+   * A set containing the sources referenced by 'part' directives.
+   */
+  HashSet<Source> _includedSources = new HashSet<Source>();
+
+  /**
+   * The errors that were produced by scanning and parsing the source.
+   */
+  List<AnalysisError> _errors = AnalysisError.NO_ERRORS;
+
+  /**
+   * Initialize a newly created task to perform analysis within the given context.
+   *
+   * @param context the context in which the task is to be performed
+   * @param source the source to be parsed
+   * @param tokenStream the head of the token stream used for parsing
+   * @param lineInfo the line information associated with the source
+   */
+  ParseDartTask(InternalAnalysisContext context, this.source, this._tokenStream,
+      this.lineInfo)
+      : super(context);
+
+  /**
+   * Return the compilation unit that was produced by parsing the source, or `null` if the
+   * task has not yet been performed or if an exception occurred.
+   *
+   * @return the compilation unit that was produced by parsing the source
+   */
+  CompilationUnit get compilationUnit => _unit;
+
+  /**
+   * Return the errors that were produced by scanning and parsing the source, or an empty list if
+   * the task has not yet been performed or if an exception occurred.
+   *
+   * @return the errors that were produced by scanning and parsing the source
+   */
+  List<AnalysisError> get errors => _errors;
+
+  /**
+   * Return a list containing the sources referenced by 'export' directives, or an empty list if
+   * the task has not yet been performed or if an exception occurred.
+   *
+   * @return an list containing the sources referenced by 'export' directives
+   */
+  List<Source> get exportedSources => _toArray(_exportedSources);
+
+  /**
+   * Return `true` if the source contains any directive other than a 'part of' directive, or
+   * `false` if the task has not yet been performed or if an exception occurred.
+   *
+   * @return `true` if the source contains any directive other than a 'part of' directive
+   */
+  bool get hasNonPartOfDirective => _containsNonPartOfDirective;
+
+  /**
+   * Return `true` if the source contains a 'part of' directive, or `false` if the task
+   * has not yet been performed or if an exception occurred.
+   *
+   * @return `true` if the source contains a 'part of' directive
+   */
+  bool get hasPartOfDirective => _containsPartOfDirective;
+
+  /**
+   * Return a list containing the sources referenced by 'import' directives, or an empty list if
+   * the task has not yet been performed or if an exception occurred.
+   *
+   * @return a list containing the sources referenced by 'import' directives
+   */
+  List<Source> get importedSources => _toArray(_importedSources);
+
+  /**
+   * Return a list containing the sources referenced by 'part' directives, or an empty list if
+   * the task has not yet been performed or if an exception occurred.
+   *
+   * @return a list containing the sources referenced by 'part' directives
+   */
+  List<Source> get includedSources => _toArray(_includedSources);
+
+  @override
+  String get taskDescription {
+    if (source == null) {
+      return "parse as dart null source";
+    }
+    return "parse as dart ${source.fullName}";
+  }
+
+  @override
+  accept(AnalysisTaskVisitor visitor) => visitor.visitParseDartTask(this);
+
+  @override
+  void internalPerform() {
+    //
+    // Then parse the token stream.
+    //
+    PerformanceStatistics.parse.makeCurrentWhile(() {
+      RecordingErrorListener errorListener = new RecordingErrorListener();
+      Parser parser = new Parser(source, errorListener);
+      AnalysisOptions options = context.analysisOptions;
+      parser.parseFunctionBodies =
+          options.analyzeFunctionBodiesPredicate(source);
+      parser.parseGenericMethods = options.enableGenericMethods;
+      _unit = parser.parseCompilationUnit(_tokenStream);
+      _unit.lineInfo = lineInfo;
+      AnalysisContext analysisContext = context;
+      for (Directive directive in _unit.directives) {
+        if (directive is PartOfDirective) {
+          _containsPartOfDirective = true;
+        } else {
+          _containsNonPartOfDirective = true;
+          if (directive is UriBasedDirective) {
+            Source referencedSource = resolveDirective(
+                analysisContext, source, directive, errorListener);
+            if (referencedSource != null) {
+              if (directive is ExportDirective) {
+                _exportedSources.add(referencedSource);
+              } else if (directive is ImportDirective) {
+                _importedSources.add(referencedSource);
+              } else if (directive is PartDirective) {
+                if (referencedSource != source) {
+                  _includedSources.add(referencedSource);
+                }
+              } else {
+                throw new AnalysisException(
+                    "$runtimeType failed to handle a ${directive.runtimeType}");
+              }
+            }
+          }
+        }
+      }
+      _errors = errorListener.getErrorsForSource(source);
+    });
+  }
+
+  /**
+   * Efficiently convert the given set of [sources] to a list.
+   */
+  List<Source> _toArray(HashSet<Source> sources) {
+    int size = sources.length;
+    if (size == 0) {
+      return Source.EMPTY_LIST;
+    }
+    return new List.from(sources);
+  }
+
+  /**
+   * Return the result of resolving the URI of the given URI-based directive against the URI of the
+   * given library, or `null` if the URI is not valid.
+   *
+   * @param context the context in which the resolution is to be performed
+   * @param librarySource the source representing the library containing the directive
+   * @param directive the directive which URI should be resolved
+   * @param errorListener the error listener to which errors should be reported
+   * @return the result of resolving the URI against the URI of the library
+   */
+  static Source resolveDirective(AnalysisContext context, Source librarySource,
+      UriBasedDirective directive, AnalysisErrorListener errorListener) {
+    StringLiteral uriLiteral = directive.uri;
+    String uriContent = uriLiteral.stringValue;
+    if (uriContent != null) {
+      uriContent = uriContent.trim();
+      directive.uriContent = uriContent;
+    }
+    UriValidationCode code = directive.validate();
+    if (code == null) {
+      String encodedUriContent = Uri.encodeFull(uriContent);
+      try {
+        Source source =
+            context.sourceFactory.resolveUri(librarySource, encodedUriContent);
+        directive.source = source;
+        return source;
+      } on JavaIOException {
+        code = UriValidationCode.INVALID_URI;
+      }
+    }
+    if (code == UriValidationCode.URI_WITH_DART_EXT_SCHEME) {
+      return null;
+    }
+    if (code == UriValidationCode.URI_WITH_INTERPOLATION) {
+      errorListener.onError(new AnalysisError(librarySource, uriLiteral.offset,
+          uriLiteral.length, CompileTimeErrorCode.URI_WITH_INTERPOLATION));
+      return null;
+    }
+    if (code == UriValidationCode.INVALID_URI) {
+      errorListener.onError(new AnalysisError(librarySource, uriLiteral.offset,
+          uriLiteral.length, CompileTimeErrorCode.INVALID_URI, [uriContent]));
+      return null;
+    }
+    throw new RuntimeException(
+        message: "Failed to handle validation code: $code");
+  }
+}
+
+/**
+ * Instances of the class `ParseHtmlTask` parse a specific source as an HTML file.
+ */
+class ParseHtmlTask extends AnalysisTask {
+  /**
+   * The name of the 'src' attribute in a HTML tag.
+   */
+  static String _ATTRIBUTE_SRC = "src";
+
+  /**
+   * The name of the 'script' tag in an HTML file.
+   */
+  static String _TAG_SCRIPT = "script";
+
+  /**
+   * The source to be parsed.
+   */
+  final Source source;
+
+  /**
+   * The contents of the source.
+   */
+  final String _content;
+
+  /**
+   * The line information that was produced.
+   */
+  LineInfo _lineInfo;
+
+  /**
+   * The HTML unit that was produced by parsing the source.
+   */
+  ht.HtmlUnit _unit;
+
+  /**
+   * The errors that were produced by scanning and parsing the source.
+   */
+  List<AnalysisError> _errors = AnalysisError.NO_ERRORS;
+
+  /**
+   * A list containing the sources of the libraries that are referenced within the HTML.
+   */
+  List<Source> _referencedLibraries = Source.EMPTY_LIST;
+
+  /**
+   * Initialize a newly created task to perform analysis within the given context.
+   *
+   * @param context the context in which the task is to be performed
+   * @param source the source to be parsed
+   * @param content the contents of the source
+   */
+  ParseHtmlTask(InternalAnalysisContext context, this.source, this._content)
+      : super(context);
+
+  /**
+   * Return the errors that were produced by scanning and parsing the source, or `null` if the
+   * task has not yet been performed or if an exception occurred.
+   *
+   * @return the errors that were produced by scanning and parsing the source
+   */
+  List<AnalysisError> get errors => _errors;
+
+  /**
+   * Return the HTML unit that was produced by parsing the source.
+   *
+   * @return the HTML unit that was produced by parsing the source
+   */
+  ht.HtmlUnit get htmlUnit => _unit;
+
+  /**
+   * Return the sources of libraries that are referenced in the specified HTML file.
+   *
+   * @return the sources of libraries that are referenced in the HTML file
+   */
+  List<Source> get librarySources {
+    List<Source> libraries = new List<Source>();
+    _unit.accept(new ParseHtmlTask_getLibrarySources(this, libraries));
+    if (libraries.isEmpty) {
+      return Source.EMPTY_LIST;
+    }
+    return libraries;
+  }
+
+  /**
+   * Return the line information that was produced, or `null` if the task has not yet been
+   * performed or if an exception occurred.
+   *
+   * @return the line information that was produced
+   */
+  LineInfo get lineInfo => _lineInfo;
+
+  /**
+   * Return a list containing the sources of the libraries that are referenced within the HTML.
+   *
+   * @return the sources of the libraries that are referenced within the HTML
+   */
+  List<Source> get referencedLibraries => _referencedLibraries;
+
+  @override
+  String get taskDescription {
+    if (source == null) {
+      return "parse as html null source";
+    }
+    return "parse as html ${source.fullName}";
+  }
+
+  @override
+  accept(AnalysisTaskVisitor visitor) => visitor.visitParseHtmlTask(this);
+
+  @override
+  void internalPerform() {
+    try {
+      ht.AbstractScanner scanner = new ht.StringScanner(source, _content);
+      scanner.passThroughElements = <String>[_TAG_SCRIPT];
+      ht.Token token = scanner.tokenize();
+      _lineInfo = new LineInfo(scanner.lineStarts);
+      RecordingErrorListener errorListener = new RecordingErrorListener();
+      _unit = new ht.HtmlParser(source, errorListener, context.analysisOptions)
+          .parse(token, _lineInfo);
+      _unit.accept(new RecursiveXmlVisitor_ParseHtmlTask_internalPerform(
+          this, errorListener));
+      _errors = errorListener.getErrorsForSource(source);
+      _referencedLibraries = librarySources;
+    } catch (exception, stackTrace) {
+      throw new AnalysisException(
+          "Exception", new CaughtException(exception, stackTrace));
+    }
+  }
+
+  /**
+   * Resolves directives in the given [CompilationUnit].
+   */
+  void _resolveScriptDirectives(
+      CompilationUnit script, AnalysisErrorListener errorListener) {
+    if (script == null) {
+      return;
+    }
+    AnalysisContext analysisContext = context;
+    for (Directive directive in script.directives) {
+      if (directive is UriBasedDirective) {
+        ParseDartTask.resolveDirective(
+            analysisContext, source, directive, errorListener);
+      }
+    }
+  }
+}
+
+class ParseHtmlTask_getLibrarySources extends ht.RecursiveXmlVisitor<Object> {
+  final ParseHtmlTask _task;
+
+  List<Source> libraries;
+
+  ParseHtmlTask_getLibrarySources(this._task, this.libraries) : super();
+
+  @override
+  Object visitHtmlScriptTagNode(ht.HtmlScriptTagNode node) {
+    ht.XmlAttributeNode scriptAttribute = null;
+    for (ht.XmlAttributeNode attribute in node.attributes) {
+      if (javaStringEqualsIgnoreCase(
+          attribute.name, ParseHtmlTask._ATTRIBUTE_SRC)) {
+        scriptAttribute = attribute;
+      }
+    }
+    if (scriptAttribute != null) {
+      try {
+        Uri uri = Uri.parse(scriptAttribute.text);
+        String fileName = uri.path;
+        Source librarySource =
+            _task.context.sourceFactory.resolveUri(_task.source, fileName);
+        if (_task.context.exists(librarySource)) {
+          libraries.add(librarySource);
+        }
+      } on FormatException {
+        // ignored - invalid URI reported during resolution phase
+      }
+    }
+    return super.visitHtmlScriptTagNode(node);
+  }
+}
+
+/**
+ * An object that manages the partitions that can be shared between analysis
+ * contexts.
+ */
+class PartitionManager {
+  /**
+   * The default cache size for a Dart SDK partition.
+   */
+  static int _DEFAULT_SDK_CACHE_SIZE = 256;
+
+  /**
+   * A table mapping SDK's to the partitions used for those SDK's.
+   */
+  HashMap<DartSdk, SdkCachePartition> _sdkPartitions =
+      new HashMap<DartSdk, SdkCachePartition>();
+
+  /**
+   * Clear any cached data being maintained by this manager.
+   */
+  void clearCache() {
+    _sdkPartitions.clear();
+  }
+
+  /**
+   * Return the partition being used for the given [sdk], creating the partition
+   * if necessary.
+   */
+  SdkCachePartition forSdk(DartSdk sdk) {
+    // Call sdk.context now, because when it creates a new
+    // InternalAnalysisContext instance, it calls forSdk() again, so creates an
+    // SdkCachePartition instance.
+    // So, if we initialize context after "partition == null", we end up
+    // with two SdkCachePartition instances.
+    InternalAnalysisContext sdkContext = sdk.context;
+    // Check cache for an existing partition.
+    SdkCachePartition partition = _sdkPartitions[sdk];
+    if (partition == null) {
+      partition = new SdkCachePartition(sdkContext, _DEFAULT_SDK_CACHE_SIZE);
+      _sdkPartitions[sdk] = partition;
+    }
+    return partition;
+  }
+}
+
+/**
+ * Representation of a pending computation which is based on the results of
+ * analysis that may or may not have been completed.
+ */
+class PendingFuture<T> {
+  /**
+   * The context in which this computation runs.
+   */
+  final AnalysisContextImpl _context;
+
+  /**
+   * The source used by this computation to compute its value.
+   */
+  final Source source;
+
+  /**
+   * The function which implements the computation.
+   */
+  final PendingFutureComputer<T> _computeValue;
+
+  /**
+   * The completer that should be completed once the computation has succeeded.
+   */
+  CancelableCompleter<T> _completer;
+
+  PendingFuture(this._context, this.source, this._computeValue) {
+    _completer = new CancelableCompleter<T>(_onCancel);
+  }
+
+  /**
+   * Retrieve the future which will be completed when this object is
+   * successfully evaluated.
+   */
+  CancelableFuture<T> get future => _completer.future;
+
+  /**
+   * Execute [_computeValue], passing it the given [sourceEntry], and complete
+   * the pending future if it's appropriate to do so.  If the pending future is
+   * completed by this call, true is returned; otherwise false is returned.
+   *
+   * Once this function has returned true, it should not be called again.
+   *
+   * Other than completing the future, this method is free of side effects.
+   * Note that any code the client has attached to the future will be executed
+   * in a microtask, so there is no danger of side effects occurring due to
+   * client callbacks.
+   */
+  bool evaluate(SourceEntry sourceEntry) {
+    assert(!_completer.isCompleted);
+    try {
+      T result = _computeValue(sourceEntry);
+      if (result == null) {
+        return false;
+      } else {
+        _completer.complete(result);
+        return true;
+      }
+    } catch (exception, stackTrace) {
+      _completer.completeError(exception, stackTrace);
+      return true;
+    }
+  }
+
+  /**
+   * No further analysis updates are expected which affect this future, so
+   * complete it with an AnalysisNotScheduledError in order to avoid
+   * deadlocking the client.
+   */
+  void forciblyComplete() {
+    try {
+      throw new AnalysisNotScheduledError();
+    } catch (exception, stackTrace) {
+      _completer.completeError(exception, stackTrace);
+    }
+  }
+
+  void _onCancel() {
+    _context._cancelFuture(this);
+  }
+}
+
+/**
+ * Container with global [AnalysisContext] performance statistics.
+ */
+class PerformanceStatistics {
+  /**
+   * The [PerformanceTag] for time spent in reading files.
+   */
+  static PerformanceTag io = new PerformanceTag('io');
+
+  /**
+   * The [PerformanceTag] for time spent in scanning.
+   */
+  static PerformanceTag scan = new PerformanceTag('scan');
+
+  /**
+   * The [PerformanceTag] for time spent in parsing.
+   */
+  static PerformanceTag parse = new PerformanceTag('parse');
+
+  /**
+   * The [PerformanceTag] for time spent in resolving.
+   */
+  static PerformanceTag resolve = new PerformanceTag('resolve');
+
+  /**
+   * The [PerformanceTag] for time spent in error verifier.
+   */
+  static PerformanceTag errors = new PerformanceTag('errors');
+
+  /**
+   * The [PerformanceTag] for time spent in hints generator.
+   */
+  static PerformanceTag hints = new PerformanceTag('hints');
+
+  /**
+   * The [PerformanceTag] for time spent in linting.
+   */
+  static PerformanceTag lint = new PerformanceTag('lint');
+
+  /**
+   * The [PerformanceTag] for time spent computing cycles.
+   */
+  static PerformanceTag cycles = new PerformanceTag('cycles');
+
+  /**
+   * The [PerformanceTag] for time spent in other phases of analysis.
+   */
+  static PerformanceTag performAnaysis = new PerformanceTag('performAnaysis');
+
+  /**
+   * The [PerformanceTag] for time spent in the analysis task visitor after
+   * tasks are complete.
+   */
+  static PerformanceTag analysisTaskVisitor =
+      new PerformanceTag('analysisTaskVisitor');
+
+  /**
+   * The [PerformanceTag] for time spent in the getter
+   * AnalysisContextImpl.nextAnalysisTask.
+   */
+  static var nextTask = new PerformanceTag('nextAnalysisTask');
+
+  /**
+   * The [PerformanceTag] for time spent during otherwise not accounted parts
+   * incremental of analysis.
+   */
+  static PerformanceTag incrementalAnalysis =
+      new PerformanceTag('incrementalAnalysis');
+}
+
+/**
+ * An error listener that will record the errors that are reported to it in a
+ * way that is appropriate for caching those errors within an analysis context.
+ */
+class RecordingErrorListener implements AnalysisErrorListener {
+  /**
+   * A map of sets containing the errors that were collected, keyed by each
+   * source.
+   */
+  Map<Source, HashSet<AnalysisError>> _errors =
+      new HashMap<Source, HashSet<AnalysisError>>();
+
+  /**
+   * Return the errors collected by the listener.
+   */
+  List<AnalysisError> get errors {
+    int numEntries = _errors.length;
+    if (numEntries == 0) {
+      return AnalysisError.NO_ERRORS;
+    }
+    List<AnalysisError> resultList = new List<AnalysisError>();
+    for (HashSet<AnalysisError> errors in _errors.values) {
+      resultList.addAll(errors);
+    }
+    return resultList;
+  }
+
+  /**
+   * Add all of the errors recorded by the given [listener] to this listener.
+   */
+  void addAll(RecordingErrorListener listener) {
+    for (AnalysisError error in listener.errors) {
+      onError(error);
+    }
+  }
+
+  /**
+   * Return the errors collected by the listener for the given [source].
+   */
+  List<AnalysisError> getErrorsForSource(Source source) {
+    HashSet<AnalysisError> errorsForSource = _errors[source];
+    if (errorsForSource == null) {
+      return AnalysisError.NO_ERRORS;
+    } else {
+      return new List.from(errorsForSource);
+    }
+  }
+
+  @override
+  void onError(AnalysisError error) {
+    Source source = error.source;
+    HashSet<AnalysisError> errorsForSource = _errors[source];
+    if (_errors[source] == null) {
+      errorsForSource = new HashSet<AnalysisError>();
+      _errors[source] = errorsForSource;
+    }
+    errorsForSource.add(error);
+  }
+}
+
+class RecursiveXmlVisitor_ParseHtmlTask_internalPerform
+    extends ht.RecursiveXmlVisitor<Object> {
+  final ParseHtmlTask ParseHtmlTask_this;
+
+  RecordingErrorListener errorListener;
+
+  RecursiveXmlVisitor_ParseHtmlTask_internalPerform(
+      this.ParseHtmlTask_this, this.errorListener)
+      : super();
+
+  @override
+  Object visitHtmlScriptTagNode(ht.HtmlScriptTagNode node) {
+    ParseHtmlTask_this._resolveScriptDirectives(node.script, errorListener);
+    return null;
+  }
+}
+
+class RecursiveXmlVisitor_ResolveHtmlTask_internalPerform
+    extends ht.RecursiveXmlVisitor<Object> {
+  final ResolveHtmlTask ResolveHtmlTask_this;
+
+  RecordingErrorListener errorListener;
+
+  RecursiveXmlVisitor_ResolveHtmlTask_internalPerform(
+      this.ResolveHtmlTask_this, this.errorListener)
+      : super();
+
+  @override
+  Object visitHtmlScriptTagNode(ht.HtmlScriptTagNode node) {
+    CompilationUnit script = node.script;
+    if (script != null) {
+      GenerateDartErrorsTask.validateDirectives(ResolveHtmlTask_this.context,
+          ResolveHtmlTask_this.source, script, errorListener);
+    }
+    return null;
+  }
+}
+
+/**
+ * An visitor that removes any resolution information from an AST structure when
+ * used to visit that structure.
+ */
+class ResolutionEraser extends GeneralizingAstVisitor<Object> {
+  @override
+  Object visitAssignmentExpression(AssignmentExpression node) {
+    node.staticElement = null;
+    node.propagatedElement = null;
+    return super.visitAssignmentExpression(node);
+  }
+
+  @override
+  Object visitBinaryExpression(BinaryExpression node) {
+    node.staticElement = null;
+    node.propagatedElement = null;
+    return super.visitBinaryExpression(node);
+  }
+
+  @override
+  Object visitBreakStatement(BreakStatement node) {
+    node.target = null;
+    return super.visitBreakStatement(node);
+  }
+
+  @override
+  Object visitCompilationUnit(CompilationUnit node) {
+    node.element = null;
+    return super.visitCompilationUnit(node);
+  }
+
+  @override
+  Object visitConstructorDeclaration(ConstructorDeclaration node) {
+    node.element = null;
+    return super.visitConstructorDeclaration(node);
+  }
+
+  @override
+  Object visitConstructorName(ConstructorName node) {
+    node.staticElement = null;
+    return super.visitConstructorName(node);
+  }
+
+  @override
+  Object visitContinueStatement(ContinueStatement node) {
+    node.target = null;
+    return super.visitContinueStatement(node);
+  }
+
+  @override
+  Object visitDirective(Directive node) {
+    node.element = null;
+    return super.visitDirective(node);
+  }
+
+  @override
+  Object visitExpression(Expression node) {
+    node.staticType = null;
+    node.propagatedType = null;
+    return super.visitExpression(node);
+  }
+
+  @override
+  Object visitFunctionExpression(FunctionExpression node) {
+    node.element = null;
+    return super.visitFunctionExpression(node);
+  }
+
+  @override
+  Object visitFunctionExpressionInvocation(FunctionExpressionInvocation node) {
+    node.staticElement = null;
+    node.propagatedElement = null;
+    return super.visitFunctionExpressionInvocation(node);
+  }
+
+  @override
+  Object visitIndexExpression(IndexExpression node) {
+    node.staticElement = null;
+    node.propagatedElement = null;
+    return super.visitIndexExpression(node);
+  }
+
+  @override
+  Object visitInstanceCreationExpression(InstanceCreationExpression node) {
+    node.staticElement = null;
+    return super.visitInstanceCreationExpression(node);
+  }
+
+  @override
+  Object visitPostfixExpression(PostfixExpression node) {
+    node.staticElement = null;
+    node.propagatedElement = null;
+    return super.visitPostfixExpression(node);
+  }
+
+  @override
+  Object visitPrefixExpression(PrefixExpression node) {
+    node.staticElement = null;
+    node.propagatedElement = null;
+    return super.visitPrefixExpression(node);
+  }
+
+  @override
+  Object visitRedirectingConstructorInvocation(
+      RedirectingConstructorInvocation node) {
+    node.staticElement = null;
+    return super.visitRedirectingConstructorInvocation(node);
+  }
+
+  @override
+  Object visitSimpleIdentifier(SimpleIdentifier node) {
+    node.staticElement = null;
+    node.propagatedElement = null;
+    return super.visitSimpleIdentifier(node);
+  }
+
+  @override
+  Object visitSuperConstructorInvocation(SuperConstructorInvocation node) {
+    node.staticElement = null;
+    return super.visitSuperConstructorInvocation(node);
+  }
+
+  /**
+   * Remove any resolution information from the given AST structure.
+   */
+  static void erase(AstNode node) {
+    node.accept(new ResolutionEraser());
+  }
+}
+
+/**
+ * The information produced by resolving a compilation unit as part of a
+ * specific library.
+ */
+class ResolutionState {
+  /**
+   * The next resolution state or `null` if none.
+   */
+  ResolutionState _nextState;
+
+  /**
+   * The source for the defining compilation unit of the library that contains
+   * this unit. If this unit is the defining compilation unit for it's library,
+   * then this will be the source for this unit.
+   */
+  Source _librarySource;
+
+  /**
+   * A table mapping descriptors to the cached results for those descriptors.
+   * If there is no entry for a given descriptor then the state is implicitly
+   * [CacheState.INVALID] and the value is implicitly the default value.
+   */
+  Map<DataDescriptor, CachedResult> resultMap =
+      new HashMap<DataDescriptor, CachedResult>();
+
+  /**
+   * Flush any AST structures being maintained by this state.
+   */
+  void flushAstStructures() {
+    _flush(DartEntry.BUILT_UNIT);
+    _flush(DartEntry.RESOLVED_UNIT);
+    if (_nextState != null) {
+      _nextState.flushAstStructures();
+    }
+  }
+
+  /**
+   * Return the state of the data represented by the given [descriptor].
+   */
+  CacheState getState(DataDescriptor descriptor) {
+    CachedResult result = resultMap[descriptor];
+    if (result == null) {
+      return CacheState.INVALID;
+    }
+    return result.state;
+  }
+
+  /**
+   * Return the value of the data represented by the given [descriptor], or
+   * `null` if the data represented by the descriptor is not valid.
+   */
+  /*<V>*/ dynamic /*V*/ getValue(DataDescriptor /*<V>*/ descriptor) {
+    CachedResult result = resultMap[descriptor];
+    if (result == null) {
+      return descriptor.defaultValue;
+    }
+    return result.value;
+  }
+
+  /**
+   * Return `true` if the state of any data value is [CacheState.ERROR].
+   */
+  bool hasErrorState() {
+    for (CachedResult result in resultMap.values) {
+      if (result.state == CacheState.ERROR) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  /**
+   * Invalidate all of the resolution information associated with the compilation unit.
+   */
+  void invalidateAllResolutionInformation() {
+    _nextState = null;
+    _librarySource = null;
+    setState(DartEntry.BUILT_UNIT, CacheState.INVALID);
+    setState(DartEntry.BUILT_ELEMENT, CacheState.INVALID);
+    setState(DartEntry.HINTS, CacheState.INVALID);
+    setState(DartEntry.LINTS, CacheState.INVALID);
+    setState(DartEntry.RESOLVED_UNIT, CacheState.INVALID);
+    setState(DartEntry.RESOLUTION_ERRORS, CacheState.INVALID);
+    setState(DartEntry.VERIFICATION_ERRORS, CacheState.INVALID);
+  }
+
+  /**
+   * Record that an exception occurred while attempting to build the element
+   * model for the source associated with this state.
+   */
+  void recordBuildElementError() {
+    setState(DartEntry.BUILT_UNIT, CacheState.ERROR);
+    setState(DartEntry.BUILT_ELEMENT, CacheState.ERROR);
+    recordResolutionError();
+  }
+
+  /**
+   * Record that an exception occurred while attempting to generate hints for
+   * the source associated with this entry. This will set the state of all
+   * verification information as being in error.
+   */
+  void recordHintError() {
+    setState(DartEntry.HINTS, CacheState.ERROR);
+  }
+
+  /**
+   * Record that an exception occurred while attempting to generate lints for
+   * the source associated with this entry. This will set the state of all
+   * verification information as being in error.
+   */
+  void recordLintError() {
+    setState(DartEntry.LINTS, CacheState.ERROR);
+  }
+
+  /**
+   * Record that an exception occurred while attempting to resolve the source
+   * associated with this state.
+   */
+  void recordResolutionError() {
+    setState(DartEntry.RESOLVED_UNIT, CacheState.ERROR);
+    setState(DartEntry.RESOLUTION_ERRORS, CacheState.ERROR);
+    recordVerificationError();
+  }
+
+  /**
+   * Record that an exception occurred while attempting to scan or parse the
+   * source associated with this entry. This will set the state of all
+   * resolution-based information as being in error.
+   */
+  void recordResolutionErrorsInAllLibraries() {
+    recordBuildElementError();
+    if (_nextState != null) {
+      _nextState.recordResolutionErrorsInAllLibraries();
+    }
+  }
+
+  /**
+   * Record that an exception occurred while attempting to generate errors and
+   * warnings for the source associated with this entry. This will set the state
+   * of all verification information as being in error.
+   */
+  void recordVerificationError() {
+    setState(DartEntry.VERIFICATION_ERRORS, CacheState.ERROR);
+    recordHintError();
+  }
+
+  /**
+   * Set the state of the data represented by the given [descriptor] to the
+   * given [state].
+   */
+  void setState(DataDescriptor descriptor, CacheState state) {
+    if (state == CacheState.VALID) {
+      throw new ArgumentError("use setValue() to set the state to VALID");
+    }
+    if (state == CacheState.INVALID) {
+      resultMap.remove(descriptor);
+    } else {
+      CachedResult result =
+          resultMap.putIfAbsent(descriptor, () => new CachedResult(descriptor));
+      result.state = state;
+      if (state != CacheState.IN_PROCESS) {
+        //
+        // If the state is in-process, we can leave the current value in the
+        // cache for any 'get' methods to access.
+        //
+        result.value = descriptor.defaultValue;
+      }
+    }
+  }
+
+  /**
+   * Set the value of the data represented by the given [descriptor] to the
+   * given [value].
+   */
+  void setValue(DataDescriptor /*<V>*/ descriptor, dynamic /*V*/ value) {
+    CachedResult result =
+        resultMap.putIfAbsent(descriptor, () => new CachedResult(descriptor));
+    SourceEntry.countTransition(descriptor, result);
+    result.state = CacheState.VALID;
+    result.value = value == null ? descriptor.defaultValue : value;
+  }
+
+  /**
+   * Flush the value of the data described by the [descriptor].
+   */
+  void _flush(DataDescriptor descriptor) {
+    CachedResult result = resultMap[descriptor];
+    if (result != null && result.state == CacheState.VALID) {
+      result.state = CacheState.FLUSHED;
+      result.value = descriptor.defaultValue;
+    }
+  }
+
+  /**
+   * Write a textual representation of the difference between the old entry and
+   * this entry to the given string [buffer]. A separator will be written before
+   * the first difference if [needsSeparator] is `true`. The [oldEntry] is the
+   * entry that was replaced by this entry. Return `true` is a separator is
+   * needed before writing any subsequent differences.
+   */
+  bool _writeDiffOn(
+      StringBuffer buffer, bool needsSeparator, DartEntry oldEntry) {
+    needsSeparator = _writeStateDiffOn(buffer, needsSeparator, "resolvedUnit",
+        DartEntry.RESOLVED_UNIT, oldEntry);
+    needsSeparator = _writeStateDiffOn(buffer, needsSeparator,
+        "resolutionErrors", DartEntry.RESOLUTION_ERRORS, oldEntry);
+    needsSeparator = _writeStateDiffOn(buffer, needsSeparator,
+        "verificationErrors", DartEntry.VERIFICATION_ERRORS, oldEntry);
+    needsSeparator = _writeStateDiffOn(
+        buffer, needsSeparator, "hints", DartEntry.HINTS, oldEntry);
+    needsSeparator = _writeStateDiffOn(
+        buffer, needsSeparator, "lints", DartEntry.LINTS, oldEntry);
+    return needsSeparator;
+  }
+
+  /**
+   * Write a textual representation of this state to the given [buffer]. The
+   * result will only be used for debugging purposes.
+   */
+  void _writeOn(StringBuffer buffer) {
+    if (_librarySource != null) {
+      _writeStateOn(buffer, "builtElement", DartEntry.BUILT_ELEMENT);
+      _writeStateOn(buffer, "builtUnit", DartEntry.BUILT_UNIT);
+      _writeStateOn(buffer, "resolvedUnit", DartEntry.RESOLVED_UNIT);
+      _writeStateOn(buffer, "resolutionErrors", DartEntry.RESOLUTION_ERRORS);
+      _writeStateOn(
+          buffer, "verificationErrors", DartEntry.VERIFICATION_ERRORS);
+      _writeStateOn(buffer, "hints", DartEntry.HINTS);
+      _writeStateOn(buffer, "lints", DartEntry.LINTS);
+      if (_nextState != null) {
+        _nextState._writeOn(buffer);
+      }
+    }
+  }
+
+  /**
+   * Write a textual representation of the difference between the state of the
+   * value described by the given [descriptor] between the [oldEntry] and this
+   * entry to the given [buffer]. Return `true` if some difference was written.
+   */
+  bool _writeStateDiffOn(StringBuffer buffer, bool needsSeparator, String label,
+      DataDescriptor descriptor, SourceEntry oldEntry) {
+    CacheState oldState = oldEntry.getState(descriptor);
+    CacheState newState = getState(descriptor);
+    if (oldState != newState) {
+      if (needsSeparator) {
+        buffer.write("; ");
+      }
+      buffer.write(label);
+      buffer.write(" = ");
+      buffer.write(oldState);
+      buffer.write(" -> ");
+      buffer.write(newState);
+      return true;
+    }
+    return needsSeparator;
+  }
+
+  /**
+   * Write a textual representation of the state of the value described by the
+   * given [descriptor] to the given bugger, prefixed by the given [label] to
+   * the given [buffer].
+   */
+  void _writeStateOn(
+      StringBuffer buffer, String label, DataDescriptor descriptor) {
+    CachedResult result = resultMap[descriptor];
+    buffer.write("; ");
+    buffer.write(label);
+    buffer.write(" = ");
+    buffer.write(result == null ? CacheState.INVALID : result.state);
+  }
+}
+
+/**
+ * A compilation unit that is not referenced by any other objects. It is used by
+ * the [LibraryResolver] to resolve a library.
+ */
+class ResolvableCompilationUnit {
+  /**
+   * The source of the compilation unit.
+   */
+  final Source source;
+
+  /**
+   * The compilation unit.
+   */
+  final CompilationUnit compilationUnit;
+
+  /**
+   * Initialize a newly created holder to hold the given [source] and
+   * [compilationUnit].
+   */
+  ResolvableCompilationUnit(this.source, this.compilationUnit);
+}
+
+/**
+ * Instances of the class `ResolveDartLibraryTask` resolve a specific Dart library.
+ */
+class ResolveDartLibraryCycleTask extends AnalysisTask {
+  /**
+   * The source representing the file whose compilation unit is to be returned. TODO(brianwilkerson)
+   * This should probably be removed, but is being left in for now to ease the transition.
+   */
+  final Source unitSource;
+
+  /**
+   * The source representing the library to be resolved.
+   */
+  final Source librarySource;
+
+  /**
+   * The libraries that are part of the cycle containing the library to be resolved.
+   */
+  final List<ResolvableLibrary> _librariesInCycle;
+
+  /**
+   * The library resolver holding information about the libraries that were resolved.
+   */
+  LibraryResolver2 _resolver;
+
+  /**
+   * Initialize a newly created task to perform analysis within the given context.
+   *
+   * @param context the context in which the task is to be performed
+   * @param unitSource the source representing the file whose compilation unit is to be returned
+   * @param librarySource the source representing the library to be resolved
+   * @param librariesInCycle the libraries that are part of the cycle containing the library to be
+   *          resolved
+   */
+  ResolveDartLibraryCycleTask(InternalAnalysisContext context, this.unitSource,
+      this.librarySource, this._librariesInCycle)
+      : super(context);
+
+  /**
+   * Return the library resolver holding information about the libraries that were resolved.
+   *
+   * @return the library resolver holding information about the libraries that were resolved
+   */
+  LibraryResolver2 get libraryResolver => _resolver;
+
+  @override
+  String get taskDescription {
+    if (librarySource == null) {
+      return "resolve library null source";
+    }
+    return "resolve library ${librarySource.fullName}";
+  }
+
+  @override
+  accept(AnalysisTaskVisitor visitor) =>
+      visitor.visitResolveDartLibraryCycleTask(this);
+
+  @override
+  void internalPerform() {
+    _resolver = new LibraryResolver2(context);
+    _resolver.resolveLibrary(librarySource, _librariesInCycle);
+  }
+}
+
+/**
+ * Instances of the class `ResolveDartLibraryTask` resolve a specific Dart library.
+ */
+class ResolveDartLibraryTask extends AnalysisTask {
+  /**
+   * The source representing the file whose compilation unit is to be returned.
+   */
+  final Source unitSource;
+
+  /**
+   * The source representing the library to be resolved.
+   */
+  final Source librarySource;
+
+  /**
+   * The library resolver holding information about the libraries that were resolved.
+   */
+  LibraryResolver _resolver;
+
+  /**
+   * Initialize a newly created task to perform analysis within the given context.
+   *
+   * @param context the context in which the task is to be performed
+   * @param unitSource the source representing the file whose compilation unit is to be returned
+   * @param librarySource the source representing the library to be resolved
+   */
+  ResolveDartLibraryTask(
+      InternalAnalysisContext context, this.unitSource, this.librarySource)
+      : super(context);
+
+  /**
+   * Return the library resolver holding information about the libraries that were resolved.
+   *
+   * @return the library resolver holding information about the libraries that were resolved
+   */
+  LibraryResolver get libraryResolver => _resolver;
+
+  @override
+  String get taskDescription {
+    if (librarySource == null) {
+      return "resolve library null source";
+    }
+    return "resolve library ${librarySource.fullName}";
+  }
+
+  @override
+  accept(AnalysisTaskVisitor visitor) =>
+      visitor.visitResolveDartLibraryTask(this);
+
+  @override
+  void internalPerform() {
+    LibraryResolverFactory resolverFactory = context.libraryResolverFactory;
+    _resolver = resolverFactory == null
+        ? new LibraryResolver(context)
+        : resolverFactory(context);
+    _resolver.resolveLibrary(librarySource, true);
+  }
+}
+
+/**
+ * Instances of the class `ResolveDartUnitTask` resolve a single Dart file based on a existing
+ * element model.
+ */
+class ResolveDartUnitTask extends AnalysisTask {
+  /**
+   * The source that is to be resolved.
+   */
+  final Source source;
+
+  /**
+   * The element model for the library containing the source.
+   */
+  final LibraryElement _libraryElement;
+
+  /**
+   * The compilation unit that was resolved by this task.
+   */
+  CompilationUnit _resolvedUnit;
+
+  /**
+   * Initialize a newly created task to perform analysis within the given context.
+   *
+   * @param context the context in which the task is to be performed
+   * @param source the source to be parsed
+   * @param libraryElement the element model for the library containing the source
+   */
+  ResolveDartUnitTask(
+      InternalAnalysisContext context, this.source, this._libraryElement)
+      : super(context);
+
+  /**
+   * Return the source for the library containing the source that is to be resolved.
+   *
+   * @return the source for the library containing the source that is to be resolved
+   */
+  Source get librarySource => _libraryElement.source;
+
+  /**
+   * Return the compilation unit that was resolved by this task.
+   *
+   * @return the compilation unit that was resolved by this task
+   */
+  CompilationUnit get resolvedUnit => _resolvedUnit;
+
+  @override
+  String get taskDescription {
+    Source librarySource = _libraryElement.source;
+    if (librarySource == null) {
+      return "resolve unit null source";
+    }
+    return "resolve unit ${librarySource.fullName}";
+  }
+
+  @override
+  accept(AnalysisTaskVisitor visitor) => visitor.visitResolveDartUnitTask(this);
+
+  @override
+  void internalPerform() {
+    TypeProvider typeProvider = _libraryElement.context.typeProvider;
+    CompilationUnit unit = context.computeResolvableCompilationUnit(source);
+    if (unit == null) {
+      throw new AnalysisException(
+          "Internal error: computeResolvableCompilationUnit returned a value without a parsed Dart unit");
+    }
+    //
+    // Resolve names in declarations.
+    //
+    new DeclarationResolver().resolve(unit, _find(_libraryElement, source));
+    //
+    // Resolve the type names.
+    //
+    RecordingErrorListener errorListener = new RecordingErrorListener();
+    TypeResolverVisitor typeResolverVisitor = new TypeResolverVisitor(
+        _libraryElement, source, typeProvider, errorListener);
+    unit.accept(typeResolverVisitor);
+    //
+    // Resolve the rest of the structure
+    //
+    InheritanceManager inheritanceManager =
+        new InheritanceManager(_libraryElement);
+    ResolverVisitor resolverVisitor = new ResolverVisitor(
+        _libraryElement, source, typeProvider, errorListener,
+        inheritanceManager: inheritanceManager);
+    unit.accept(resolverVisitor);
+    //
+    // Perform additional error checking.
+    //
+    PerformanceStatistics.errors.makeCurrentWhile(() {
+      ErrorReporter errorReporter = new ErrorReporter(errorListener, source);
+      ErrorVerifier errorVerifier = new ErrorVerifier(
+          errorReporter,
+          _libraryElement,
+          typeProvider,
+          inheritanceManager,
+          context.analysisOptions.enableSuperMixins);
+      unit.accept(errorVerifier);
+      // TODO(paulberry): as a temporary workaround for issue 21572,
+      // ConstantVerifier is being run right after ConstantValueComputer, so we
+      // don't need to run it here.  Once issue 21572 is fixed, re-enable the
+      // call to ConstantVerifier.
+//       ConstantVerifier constantVerifier = new ConstantVerifier(errorReporter, _libraryElement, typeProvider);
+//       unit.accept(constantVerifier);
+    });
+    //
+    // Capture the results.
+    //
+    _resolvedUnit = unit;
+  }
+
+  /**
+   * Search the compilation units that are part of the given library and return the element
+   * representing the compilation unit with the given source. Return `null` if there is no
+   * such compilation unit.
+   *
+   * @param libraryElement the element representing the library being searched through
+   * @param unitSource the source for the compilation unit whose element is to be returned
+   * @return the element representing the compilation unit
+   */
+  CompilationUnitElement _find(
+      LibraryElement libraryElement, Source unitSource) {
+    CompilationUnitElement element = libraryElement.definingCompilationUnit;
+    if (element.source == unitSource) {
+      return element;
+    }
+    for (CompilationUnitElement partElement in libraryElement.parts) {
+      if (partElement.source == unitSource) {
+        return partElement;
+      }
+    }
+    return null;
+  }
+}
+
+/**
+ * Instances of the class `ResolveHtmlTask` resolve a specific source as an HTML file.
+ */
+class ResolveHtmlTask extends AnalysisTask {
+  /**
+   * The source to be resolved.
+   */
+  final Source source;
+
+  /**
+   * The time at which the contents of the source were last modified.
+   */
+  final int modificationTime;
+
+  /**
+   * The HTML unit to be resolved.
+   */
+  final ht.HtmlUnit _unit;
+
+  /**
+   * The [HtmlUnit] that was resolved by this task.
+   */
+  ht.HtmlUnit _resolvedUnit;
+
+  /**
+   * The element produced by resolving the source.
+   */
+  HtmlElement _element = null;
+
+  /**
+   * The resolution errors that were discovered while resolving the source.
+   */
+  List<AnalysisError> _resolutionErrors = AnalysisError.NO_ERRORS;
+
+  /**
+   * Initialize a newly created task to perform analysis within the given context.
+   *
+   * @param context the context in which the task is to be performed
+   * @param source the source to be resolved
+   * @param modificationTime the time at which the contents of the source were last modified
+   * @param unit the HTML unit to be resolved
+   */
+  ResolveHtmlTask(InternalAnalysisContext context, this.source,
+      this.modificationTime, this._unit)
+      : super(context);
+
+  HtmlElement get element => _element;
+
+  List<AnalysisError> get resolutionErrors => _resolutionErrors;
+
+  /**
+   * Return the [HtmlUnit] that was resolved by this task.
+   *
+   * @return the [HtmlUnit] that was resolved by this task
+   */
+  ht.HtmlUnit get resolvedUnit => _resolvedUnit;
+
+  @override
+  String get taskDescription {
+    if (source == null) {
+      return "resolve as html null source";
+    }
+    return "resolve as html ${source.fullName}";
+  }
+
+  @override
+  accept(AnalysisTaskVisitor visitor) => visitor.visitResolveHtmlTask(this);
+
+  @override
+  void internalPerform() {
+    //
+    // Build the standard HTML element.
+    //
+    HtmlUnitBuilder builder = new HtmlUnitBuilder(context);
+    _element = builder.buildHtmlElement(source, _unit);
+    RecordingErrorListener errorListener = builder.errorListener;
+    //
+    // Validate the directives
+    //
+    _unit.accept(new RecursiveXmlVisitor_ResolveHtmlTask_internalPerform(
+        this, errorListener));
+    //
+    // Record all resolution errors.
+    //
+    _resolutionErrors = errorListener.getErrorsForSource(source);
+    //
+    // Remember the resolved unit.
+    //
+    _resolvedUnit = _unit;
+  }
+}
+
+/**
+ * The priority of data in the cache in terms of the desirability of retaining
+ * some specified data about a specified source.
+ */
+class RetentionPriority extends Enum<RetentionPriority> {
+  /**
+   * A priority indicating that a given piece of data can be removed from the
+   * cache without reservation.
+   */
+  static const RetentionPriority LOW = const RetentionPriority('LOW', 0);
+
+  /**
+   * A priority indicating that a given piece of data should not be removed from
+   * the cache unless there are no sources for which the corresponding data has
+   * a lower priority. Currently used for data that is needed in order to finish
+   * some outstanding analysis task.
+   */
+  static const RetentionPriority MEDIUM = const RetentionPriority('MEDIUM', 1);
+
+  /**
+   * A priority indicating that a given piece of data should not be removed from
+   * the cache. Currently used for data related to a priority source.
+   */
+  static const RetentionPriority HIGH = const RetentionPriority('HIGH', 2);
+
+  static const List<RetentionPriority> values = const [LOW, MEDIUM, HIGH];
+
+  const RetentionPriority(String name, int ordinal) : super(name, ordinal);
+}
+
+/**
+ * Instances of the class `ScanDartTask` scan a specific source as a Dart file.
+ */
+class ScanDartTask extends AnalysisTask {
+  /**
+   * The source to be scanned.
+   */
+  final Source source;
+
+  /**
+   * The contents of the source.
+   */
+  final String _content;
+
+  /**
+   * The token stream that was produced by scanning the source.
+   */
+  Token _tokenStream;
+
+  /**
+   * The line information that was produced.
+   */
+  LineInfo _lineInfo;
+
+  /**
+   * The errors that were produced by scanning the source.
+   */
+  List<AnalysisError> _errors = AnalysisError.NO_ERRORS;
+
+  /**
+   * Initialize a newly created task to perform analysis within the given context.
+   *
+   * @param context the context in which the task is to be performed
+   * @param source the source to be parsed
+   * @param content the contents of the source
+   */
+  ScanDartTask(InternalAnalysisContext context, this.source, this._content)
+      : super(context);
+
+  /**
+   * Return the errors that were produced by scanning the source, or `null` if the task has
+   * not yet been performed or if an exception occurred.
+   *
+   * @return the errors that were produced by scanning the source
+   */
+  List<AnalysisError> get errors => _errors;
+
+  /**
+   * Return the line information that was produced, or `null` if the task has not yet been
+   * performed or if an exception occurred.
+   *
+   * @return the line information that was produced
+   */
+  LineInfo get lineInfo => _lineInfo;
+
+  @override
+  String get taskDescription {
+    if (source == null) {
+      return "scan as dart null source";
+    }
+    return "scan as dart ${source.fullName}";
+  }
+
+  /**
+   * Return the token stream that was produced by scanning the source, or `null` if the task
+   * has not yet been performed or if an exception occurred.
+   *
+   * @return the token stream that was produced by scanning the source
+   */
+  Token get tokenStream => _tokenStream;
+
+  @override
+  accept(AnalysisTaskVisitor visitor) => visitor.visitScanDartTask(this);
+
+  @override
+  void internalPerform() {
+    PerformanceStatistics.scan.makeCurrentWhile(() {
+      RecordingErrorListener errorListener = new RecordingErrorListener();
+      try {
+        Scanner scanner = new Scanner(
+            source, new CharSequenceReader(_content), errorListener);
+        scanner.preserveComments = context.analysisOptions.preserveComments;
+        _tokenStream = scanner.tokenize();
+        _lineInfo = new LineInfo(scanner.lineStarts);
+        _errors = errorListener.getErrorsForSource(source);
+      } catch (exception, stackTrace) {
+        throw new AnalysisException(
+            "Exception", new CaughtException(exception, stackTrace));
+      }
+    });
+  }
+}
+
+/**
+ * An [AnalysisContext] that only contains sources for a Dart SDK.
+ */
+class SdkAnalysisContext extends AnalysisContextImpl {
+  @override
+  AnalysisCache createCacheFromSourceFactory(SourceFactory factory) {
+    if (factory == null) {
+      return super.createCacheFromSourceFactory(factory);
+    }
+    DartSdk sdk = factory.dartSdk;
+    if (sdk == null) {
+      throw new IllegalArgumentException(
+          "The source factory for an SDK analysis context must have a DartUriResolver");
+    }
+    return new AnalysisCache(
+        <CachePartition>[AnalysisEngine.instance.partitionManager.forSdk(sdk)]);
+  }
+}
+
+/**
+ * A cache partition that contains all of the sources in the SDK.
+ */
+class SdkCachePartition extends CachePartition {
+  /**
+   * Initialize a newly created partition. The [context] is the context that
+   * owns this partition. The [maxCacheSize] is the maximum number of sources
+   * for which AST structures should be kept in the cache.
+   */
+  SdkCachePartition(InternalAnalysisContext context, int maxCacheSize)
+      : super(context, maxCacheSize, DefaultRetentionPolicy.POLICY);
+
+  @override
+  bool contains(Source source) => source.isInSystemLibrary;
+}
+
+/**
+ * The information cached by an analysis context about an individual source, no
+ * matter what kind of source it is.
+ */
+abstract class SourceEntry {
+  /**
+   * The data descriptor representing the contents of the source.
+   */
+  static final DataDescriptor<String> CONTENT =
+      new DataDescriptor<String>("SourceEntry.CONTENT");
+
+  /**
+   * The data descriptor representing the errors resulting from reading the
+   * source content.
+   */
+  static final DataDescriptor<List<AnalysisError>> CONTENT_ERRORS =
+      new DataDescriptor<List<AnalysisError>>(
+          "SourceEntry.CONTENT_ERRORS", AnalysisError.NO_ERRORS);
+
+  /**
+   * The data descriptor representing the line information.
+   */
+  static final DataDescriptor<LineInfo> LINE_INFO =
+      new DataDescriptor<LineInfo>("SourceEntry.LINE_INFO");
+
+  /**
+   * The index of the flag indicating whether the source was explicitly added to
+   * the context or whether the source was implicitly added because it was
+   * referenced by another source.
+   */
+  static int _EXPLICITLY_ADDED_FLAG = 0;
+
+  /**
+   * A table mapping data descriptors to a count of the number of times a value
+   * was set when in a given state.
+   */
+  static final Map<DataDescriptor, Map<CacheState, int>> transitionMap =
+      new HashMap<DataDescriptor, Map<CacheState, int>>();
+
+  /**
+   * The most recent time at which the state of the source matched the state
+   * represented by this entry.
+   */
+  int modificationTime = 0;
+
+  /**
+   * The exception that caused one or more values to have a state of
+   * [CacheState.ERROR].
+   */
+  CaughtException exception;
+
+  /**
+   * A bit-encoding of boolean flags associated with this element.
+   */
+  int _flags = 0;
+
+  /**
+   * A table mapping data descriptors to the cached results for those
+   * descriptors.
+   */
+  Map<DataDescriptor, CachedResult> resultMap =
+      new HashMap<DataDescriptor, CachedResult>();
+
+  /**
+   * Return all of the errors associated with this entry.
+   */
+  List<AnalysisError> get allErrors {
+    return getValue(CONTENT_ERRORS);
+  }
+
+  /**
+   * Get a list of all the library-independent descriptors for which values may
+   * be stored in this SourceEntry.
+   */
+  List<DataDescriptor> get descriptors {
+    return <DataDescriptor>[CONTENT, CONTENT_ERRORS, LINE_INFO];
+  }
+
+  /**
+   * Return `true` if the source was explicitly added to the context or `false`
+   * if the source was implicitly added because it was referenced by another
+   * source.
+   */
+  bool get explicitlyAdded => _getFlag(_EXPLICITLY_ADDED_FLAG);
+
+  /**
+   * Set whether the source was explicitly added to the context to match the
+   * [explicitlyAdded] flag.
+   */
+  void set explicitlyAdded(bool explicitlyAdded) {
+    _setFlag(_EXPLICITLY_ADDED_FLAG, explicitlyAdded);
+  }
+
+  /**
+   * Return the kind of the source, or `null` if the kind is not currently
+   * cached.
+   */
+  SourceKind get kind;
+
+  /**
+   * Fix the state of the [exception] to match the current state of the entry.
+   */
+  void fixExceptionState() {
+    if (hasErrorState()) {
+      if (exception == null) {
+        //
+        // This code should never be reached, but is a fail-safe in case an
+        // exception is not recorded when it should be.
+        //
+        String message = "State set to ERROR without setting an exception";
+        exception = new CaughtException(new AnalysisException(message), null);
+      }
+    } else {
+      exception = null;
+    }
+  }
+
+  /**
+   * Return a textual representation of the difference between the [oldEntry]
+   * and this entry. The difference is represented as a sequence of fields whose
+   * value would change if the old entry were converted into the new entry.
+   */
+  String getDiff(SourceEntry oldEntry) {
+    StringBuffer buffer = new StringBuffer();
+    _writeDiffOn(buffer, oldEntry);
+    return buffer.toString();
+  }
+
+  /**
+   * Return the state of the data represented by the given [descriptor].
+   */
+  CacheState getState(DataDescriptor descriptor) {
+    if (!_isValidDescriptor(descriptor)) {
+      throw new ArgumentError("Invalid descriptor: $descriptor");
+    }
+    CachedResult result = resultMap[descriptor];
+    if (result == null) {
+      return CacheState.INVALID;
+    }
+    return result.state;
+  }
+
+  /**
+   * Return the value of the data represented by the given [descriptor], or
+   * `null` if the data represented by the descriptor is not valid.
+   */
+  /*<V>*/ dynamic /*V*/ getValue(DataDescriptor /*<V>*/ descriptor) {
+    if (!_isValidDescriptor(descriptor)) {
+      throw new ArgumentError("Invalid descriptor: $descriptor");
+    }
+    CachedResult result = resultMap[descriptor];
+    if (result == null) {
+      return descriptor.defaultValue;
+    }
+    return result.value;
+  }
+
+  /**
+   * Return `true` if the state of any data value is [CacheState.ERROR].
+   */
+  bool hasErrorState() {
+    for (CachedResult result in resultMap.values) {
+      if (result.state == CacheState.ERROR) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  /**
+   * Invalidate all of the information associated with this source.
+   */
+  void invalidateAllInformation() {
+    setState(CONTENT, CacheState.INVALID);
+    setState(CONTENT_ERRORS, CacheState.INVALID);
+    setState(LINE_INFO, CacheState.INVALID);
+  }
+
+  /**
+   * Record that an [exception] occurred while attempting to get the contents of
+   * the source represented by this entry. This will set the state of all
+   * information, including any resolution-based information, as being in error.
+   */
+  void recordContentError(CaughtException exception) {
+    setState(CONTENT, CacheState.ERROR);
+    recordScanError(exception);
+  }
+
+  /**
+   * Record that an [exception] occurred while attempting to scan or parse the
+   * entry represented by this entry. This will set the state of all
+   * information, including any resolution-based information, as being in error.
+   */
+  void recordScanError(CaughtException exception) {
+    this.exception = exception;
+    setState(LINE_INFO, CacheState.ERROR);
+  }
+
+  /**
+   * Set the state of the data represented by the given [descriptor] to the
+   * given [state].
+   */
+  void setState(DataDescriptor descriptor, CacheState state) {
+    if (!_isValidDescriptor(descriptor)) {
+      throw new ArgumentError("Invalid descriptor: $descriptor");
+    }
+    if (state == CacheState.VALID) {
+      throw new ArgumentError("use setValue() to set the state to VALID");
+    }
+    _validateStateChange(descriptor, state);
+    if (state == CacheState.INVALID) {
+      resultMap.remove(descriptor);
+    } else {
+      CachedResult result =
+          resultMap.putIfAbsent(descriptor, () => new CachedResult(descriptor));
+      result.state = state;
+      if (state != CacheState.IN_PROCESS) {
+        //
+        // If the state is in-process, we can leave the current value in the
+        // cache for any 'get' methods to access.
+        //
+        result.value = descriptor.defaultValue;
+      }
+    }
+  }
+
+  /**
+   * Set the value of the data represented by the given [descriptor] to the
+   * given [value].
+   */
+  void setValue(DataDescriptor /*<V>*/ descriptor, dynamic /*V*/ value) {
+    if (!_isValidDescriptor(descriptor)) {
+      throw new ArgumentError("Invalid descriptor: $descriptor");
+    }
+    _validateStateChange(descriptor, CacheState.VALID);
+    CachedResult result =
+        resultMap.putIfAbsent(descriptor, () => new CachedResult(descriptor));
+    countTransition(descriptor, result);
+    result.state = CacheState.VALID;
+    result.value = value == null ? descriptor.defaultValue : value;
+  }
+
+  @override
+  String toString() {
+    StringBuffer buffer = new StringBuffer();
+    _writeOn(buffer);
+    return buffer.toString();
+  }
+
+  /**
+   * Flush the value of the data described by the [descriptor].
+   */
+  void _flush(DataDescriptor descriptor) {
+    CachedResult result = resultMap[descriptor];
+    if (result != null && result.state == CacheState.VALID) {
+      _validateStateChange(descriptor, CacheState.FLUSHED);
+      result.state = CacheState.FLUSHED;
+      result.value = descriptor.defaultValue;
+    }
+  }
+
+  /**
+   * Return the value of the flag with the given [index].
+   */
+  bool _getFlag(int index) => BooleanArray.get(_flags, index);
+
+  /**
+   * Return `true` if the [descriptor] is valid for this entry.
+   */
+  bool _isValidDescriptor(DataDescriptor descriptor) {
+    return descriptor == CONTENT ||
+        descriptor == CONTENT_ERRORS ||
+        descriptor == LINE_INFO;
+  }
+
+  /**
+   * Set the value of the flag with the given [index] to the given [value].
+   */
+  void _setFlag(int index, bool value) {
+    _flags = BooleanArray.set(_flags, index, value);
+  }
+
+  /**
+   * If the state of the value described by the given [descriptor] is changing
+   * from ERROR to anything else, capture the information. This is an attempt to
+   * discover the underlying cause of a long-standing bug.
+   */
+  void _validateStateChange(DataDescriptor descriptor, CacheState newState) {
+    // TODO(brianwilkerson) Decide whether we still want to capture this data.
+//    if (descriptor != CONTENT) {
+//      return;
+//    }
+//    CachedResult result = resultMap[CONTENT];
+//    if (result != null && result.state == CacheState.ERROR) {
+//      String message =
+//          "contentState changing from ${result.state} to $newState";
+//      InstrumentationBuilder builder =
+//          Instrumentation.builder2("SourceEntry-validateStateChange");
+//      builder.data3("message", message);
+//      //builder.data("source", source.getFullName());
+//      builder.record(new CaughtException(new AnalysisException(message), null));
+//      builder.log();
+//    }
+  }
+
+  /**
+   * Write a textual representation of the difference between the [oldEntry] and
+   * this entry to the given string [buffer]. Return `true` if some difference
+   * was written.
+   */
+  bool _writeDiffOn(StringBuffer buffer, SourceEntry oldEntry) {
+    bool needsSeparator = false;
+    CaughtException oldException = oldEntry.exception;
+    if (!identical(oldException, exception)) {
+      buffer.write("exception = ");
+      buffer.write(oldException.runtimeType);
+      buffer.write(" -> ");
+      buffer.write(exception.runtimeType);
+      needsSeparator = true;
+    }
+    int oldModificationTime = oldEntry.modificationTime;
+    if (oldModificationTime != modificationTime) {
+      if (needsSeparator) {
+        buffer.write("; ");
+      }
+      buffer.write("time = ");
+      buffer.write(oldModificationTime);
+      buffer.write(" -> ");
+      buffer.write(modificationTime);
+      needsSeparator = true;
+    }
+    needsSeparator =
+        _writeStateDiffOn(buffer, needsSeparator, "content", CONTENT, oldEntry);
+    needsSeparator = _writeStateDiffOn(
+        buffer, needsSeparator, "contentErrors", CONTENT_ERRORS, oldEntry);
+    needsSeparator = _writeStateDiffOn(
+        buffer, needsSeparator, "lineInfo", LINE_INFO, oldEntry);
+    return needsSeparator;
+  }
+
+  /**
+   * Write a textual representation of this entry to the given [buffer]. The
+   * result should only be used for debugging purposes.
+   */
+  void _writeOn(StringBuffer buffer) {
+    buffer.write("time = ");
+    buffer.write(modificationTime);
+    _writeStateOn(buffer, "content", CONTENT);
+    _writeStateOn(buffer, "contentErrors", CONTENT_ERRORS);
+    _writeStateOn(buffer, "lineInfo", LINE_INFO);
+  }
+
+  /**
+   * Write a textual representation of the difference between the state of the
+   * value described by the given [descriptor] between the [oldEntry] and this
+   * entry to the given [buffer]. Return `true` if some difference was written.
+   */
+  bool _writeStateDiffOn(StringBuffer buffer, bool needsSeparator, String label,
+      DataDescriptor descriptor, SourceEntry oldEntry) {
+    CacheState oldState = oldEntry.getState(descriptor);
+    CacheState newState = getState(descriptor);
+    if (oldState != newState) {
+      if (needsSeparator) {
+        buffer.write("; ");
+      }
+      buffer.write(label);
+      buffer.write(" = ");
+      buffer.write(oldState);
+      buffer.write(" -> ");
+      buffer.write(newState);
+      return true;
+    }
+    return needsSeparator;
+  }
+
+  /**
+   * Write a textual representation of the state of the value described by the
+   * given [descriptor] to the given bugger, prefixed by the given [label] to
+   * the given [buffer].
+   */
+  void _writeStateOn(
+      StringBuffer buffer, String label, DataDescriptor descriptor) {
+    CachedResult result = resultMap[descriptor];
+    buffer.write("; ");
+    buffer.write(label);
+    buffer.write(" = ");
+    buffer.write(result == null ? CacheState.INVALID : result.state);
+  }
+
+  /**
+   * Increment the count of the number of times that data represented by the
+   * given [descriptor] was transitioned from the current state (as found in the
+   * given [result] to a valid state.
+   */
+  static void countTransition(DataDescriptor descriptor, CachedResult result) {
+    Map<CacheState, int> countMap = transitionMap.putIfAbsent(
+        descriptor, () => new HashMap<CacheState, int>());
+    int count = countMap[result.state];
+    countMap[result.state] = count == null ? 1 : count + 1;
+  }
+}
+
+/**
+ * The priority levels used to return sources in an optimal order. A smaller
+ * ordinal value equates to a higher priority.
+ */
+class SourcePriority extends Enum<SourcePriority> {
+  /**
+   * Used for a Dart source that is known to be a part contained in a library
+   * that was recently resolved. These parts are given a higher priority because
+   * there is a high probability that their AST structure is still in the cache
+   * and therefore would not need to be re-created.
+   */
+  static const SourcePriority PRIORITY_PART =
+      const SourcePriority('PRIORITY_PART', 0);
+
+  /**
+   * Used for a Dart source that is known to be a library.
+   */
+  static const SourcePriority LIBRARY = const SourcePriority('LIBRARY', 1);
+
+  /**
+   * Used for a Dart source whose kind is unknown.
+   */
+  static const SourcePriority UNKNOWN = const SourcePriority('UNKNOWN', 2);
+
+  /**
+   * Used for a Dart source that is known to be a part but whose library has not
+   * yet been resolved.
+   */
+  static const SourcePriority NORMAL_PART =
+      const SourcePriority('NORMAL_PART', 3);
+
+  /**
+   * Used for an HTML source.
+   */
+  static const SourcePriority HTML = const SourcePriority('HTML', 4);
+
+  static const List<SourcePriority> values = const [
+    PRIORITY_PART,
+    LIBRARY,
+    UNKNOWN,
+    NORMAL_PART,
+    HTML
+  ];
+
+  const SourcePriority(String name, int ordinal) : super(name, ordinal);
+}
+
+/**
+ * [SourcesChangedEvent] indicates which sources have been added, removed,
+ * or whose contents have changed.
+ */
+class SourcesChangedEvent {
+  /**
+   * The internal representation of what has changed. Clients should not access
+   * this field directly.
+   */
+  final ChangeSet _changeSet;
+
+  /**
+   * Construct an instance representing the given changes.
+   */
+  SourcesChangedEvent(ChangeSet changeSet) : _changeSet = changeSet;
+
+  /**
+   * Construct an instance representing a source content change.
+   */
+  factory SourcesChangedEvent.changedContent(Source source, String contents) {
+    ChangeSet changeSet = new ChangeSet();
+    changeSet.changedContent(source, contents);
+    return new SourcesChangedEvent(changeSet);
+  }
+
+  /**
+   * Construct an instance representing a source content change.
+   */
+  factory SourcesChangedEvent.changedRange(Source source, String contents,
+      int offset, int oldLength, int newLength) {
+    ChangeSet changeSet = new ChangeSet();
+    changeSet.changedRange(source, contents, offset, oldLength, newLength);
+    return new SourcesChangedEvent(changeSet);
+  }
+
+  /**
+   * Return the collection of sources for which content has changed.
+   */
+  Iterable<Source> get changedSources {
+    List<Source> changedSources = new List.from(_changeSet.changedSources);
+    changedSources.addAll(_changeSet.changedContents.keys);
+    changedSources.addAll(_changeSet.changedRanges.keys);
+    return changedSources;
+  }
+
+  /**
+   * Return `true` if any sources were added.
+   */
+  bool get wereSourcesAdded => _changeSet.addedSources.length > 0;
+
+  /**
+   * Return `true` if any sources were removed or deleted.
+   */
+  bool get wereSourcesRemovedOrDeleted =>
+      _changeSet.removedSources.length > 0 ||
+          _changeSet.removedContainers.length > 0 ||
+          _changeSet.deletedSources.length > 0;
+}
+
+/**
+ * Analysis data for which we have a modification time.
+ */
+class TimestampedData<E> {
+  /**
+   * The modification time of the source from which the data was created.
+   */
+  final int modificationTime;
+
+  /**
+   * The data that was created from the source.
+   */
+  final E data;
+
+  /**
+   * Initialize a newly created holder to associate the given [data] with the
+   * given [modificationTime].
+   */
+  TimestampedData(this.modificationTime, this.data);
+}
+
+/**
+ * A cache partition that contains all sources not contained in other
+ * partitions.
+ */
+class UniversalCachePartition extends CachePartition {
+  /**
+   * Initialize a newly created partition. The [context] is the context that
+   * owns this partition. The [maxCacheSize] is the maximum number of sources
+   * for which AST structures should be kept in the cache. The [retentionPolicy]
+   * is the policy used to determine which pieces of data to remove from the
+   * cache.
+   */
+  UniversalCachePartition(InternalAnalysisContext context, int maxCacheSize,
+      CacheRetentionPolicy retentionPolicy)
+      : super(context, maxCacheSize, retentionPolicy);
+
+  @override
+  bool contains(Source source) => true;
+}
+
+/**
+ * The unique instances of the class `WaitForAsyncTask` represents a state in which there is
+ * no analysis work that can be done until some asynchronous task (such as IO) has completed, but
+ * where analysis is not yet complete.
+ */
+class WaitForAsyncTask extends AnalysisTask {
+  /**
+   * The unique instance of this class.
+   */
+  static WaitForAsyncTask _UniqueInstance = new WaitForAsyncTask();
+
+  /**
+   * Return the unique instance of this class.
+   *
+   * @return the unique instance of this class
+   */
+  static WaitForAsyncTask get instance => _UniqueInstance;
+
+  /**
+   * Prevent the creation of instances of this class.
+   */
+  WaitForAsyncTask() : super(null);
+
+  @override
+  String get taskDescription => "Waiting for async analysis";
+
+  @override
+  accept(AnalysisTaskVisitor visitor) => null;
+
+  @override
+  void internalPerform() {
+    // There is no work to be done.
+  }
+}
+
+/**
+ * An object that manages a list of sources that need to have analysis work
+ * performed on them.
+ */
+class WorkManager {
+  /**
+   * A list containing the various queues is priority order.
+   */
+  List<List<Source>> _workQueues;
+
+  /**
+   * Initialize a newly created manager to have no work queued up.
+   */
+  WorkManager() {
+    int queueCount = SourcePriority.values.length;
+    _workQueues = new List<List<Source>>(queueCount);
+    for (int i = 0; i < queueCount; i++) {
+      _workQueues[i] = new List<Source>();
+    }
+  }
+
+  /**
+   * Record that the given [source] needs to be analyzed. The [priority] level
+   * is used to control when the source will be analyzed with respect to other
+   * sources. If the source was previously added then it's priority is updated.
+   * If it was previously added with the same priority then it's position in the
+   * queue is unchanged.
+   */
+  void add(Source source, SourcePriority priority) {
+    int queueCount = _workQueues.length;
+    int ordinal = priority.ordinal;
+    for (int i = 0; i < queueCount; i++) {
+      List<Source> queue = _workQueues[i];
+      if (i == ordinal) {
+        if (!queue.contains(source)) {
+          queue.add(source);
+        }
+      } else {
+        queue.remove(source);
+      }
+    }
+  }
+
+  /**
+   * Record that the given [source] needs to be analyzed. The [priority] level
+   * is used to control when the source will be analyzed with respect to other
+   * sources. If the source was previously added then it's priority is updated.
+   * In either case, it will be analyzed before other sources of the same
+   * priority.
+   */
+  void addFirst(Source source, SourcePriority priority) {
+    int queueCount = _workQueues.length;
+    int ordinal = priority.ordinal;
+    for (int i = 0; i < queueCount; i++) {
+      List<Source> queue = _workQueues[i];
+      if (i == ordinal) {
+        queue.remove(source);
+        queue.insert(0, source);
+      } else {
+        queue.remove(source);
+      }
+    }
+  }
+
+  /**
+   * Return an iterator that can be used to access the sources to be analyzed in
+   * the order in which they should be analyzed.
+   *
+   * <b>Note:</b> As with other iterators, no sources can be added or removed
+   * from this work manager while the iterator is being used. Unlike some
+   * implementations, however, the iterator will not detect when this
+   * requirement has been violated; it might work correctly, it might return the
+   * wrong source, or it might throw an exception.
+   */
+  WorkManager_WorkIterator iterator() => new WorkManager_WorkIterator(this);
+
+  /**
+   * Record that the given source is fully analyzed.
+   */
+  void remove(Source source) {
+    int queueCount = _workQueues.length;
+    for (int i = 0; i < queueCount; i++) {
+      _workQueues[i].remove(source);
+    }
+  }
+
+  @override
+  String toString() {
+    StringBuffer buffer = new StringBuffer();
+    List<SourcePriority> priorities = SourcePriority.values;
+    bool needsSeparator = false;
+    int queueCount = _workQueues.length;
+    for (int i = 0; i < queueCount; i++) {
+      List<Source> queue = _workQueues[i];
+      if (!queue.isEmpty) {
+        if (needsSeparator) {
+          buffer.write("; ");
+        }
+        buffer.write(priorities[i]);
+        buffer.write(": ");
+        int queueSize = queue.length;
+        for (int j = 0; j < queueSize; j++) {
+          if (j > 0) {
+            buffer.write(", ");
+          }
+          buffer.write(queue[j].fullName);
+        }
+        needsSeparator = true;
+      }
+    }
+    return buffer.toString();
+  }
+}
+
+/**
+ * An iterator that returns the sources in a work manager in the order in which
+ * they are to be analyzed.
+ */
+class WorkManager_WorkIterator {
+  final WorkManager _manager;
+
+  /**
+   * The index of the work queue through which we are currently iterating.
+   */
+  int _queueIndex = 0;
+
+  /**
+   * The index of the next element of the work queue to be returned.
+   */
+  int _index = -1;
+
+  /**
+   * Initialize a newly created iterator to be ready to return the first element
+   * in the iteration.
+   */
+  WorkManager_WorkIterator(this._manager) {
+    _advance();
+  }
+
+  /**
+   * Return `true` if there is another [Source] available for processing.
+   */
+  bool get hasNext => _queueIndex < _manager._workQueues.length;
+
+  /**
+   * Return the next [Source] available for processing and advance so that the
+   * returned source will not be returned again.
+   */
+  Source next() {
+    if (!hasNext) {
+      throw new NoSuchElementException();
+    }
+    Source source = _manager._workQueues[_queueIndex][_index];
+    _advance();
+    return source;
+  }
+
+  /**
+   * Increment the [index] and [queueIndex] so that they are either indicating
+   * the next source to be returned or are indicating that there are no more
+   * sources to be returned.
+   */
+  void _advance() {
+    _index++;
+    if (_index >= _manager._workQueues[_queueIndex].length) {
+      _index = 0;
+      _queueIndex++;
+      while (_queueIndex < _manager._workQueues.length &&
+          _manager._workQueues[_queueIndex].isEmpty) {
+        _queueIndex++;
+      }
+    }
+  }
+}
+
+/**
+ * A helper class used to create futures for AnalysisContextImpl. Using a helper
+ * class allows us to preserve the generic parameter T.
+ */
+class _AnalysisFutureHelper<T> {
+  final AnalysisContextImpl _context;
+
+  _AnalysisFutureHelper(this._context);
+
+  /**
+   * Return a future that will be completed with the result of calling
+   * [computeValue].  If [computeValue] returns non-null, the future will be
+   * completed immediately with the resulting value.  If it returns null, then
+   * it will be re-executed in the future, after the next time the cached
+   * information for [source] has changed.  If [computeValue] throws an
+   * exception, the future will fail with that exception.
+   *
+   * If the [computeValue] still returns null after there is no further
+   * analysis to be done for [source], then the future will be completed with
+   * the error AnalysisNotScheduledError.
+   *
+   * Since [computeValue] will be called while the state of analysis is being
+   * updated, it should be free of side effects so that it doesn't cause
+   * reentrant changes to the analysis state.
+   */
+  CancelableFuture<T> computeAsync(
+      Source source, T computeValue(SourceEntry sourceEntry)) {
+    if (_context.isDisposed) {
+      // No further analysis is expected, so return a future that completes
+      // immediately with AnalysisNotScheduledError.
+      return new CancelableFuture.error(new AnalysisNotScheduledError());
+    }
+    SourceEntry sourceEntry = _context.getReadableSourceEntryOrNull(source);
+    if (sourceEntry == null) {
+      return new CancelableFuture.error(new AnalysisNotScheduledError());
+    }
+    PendingFuture pendingFuture =
+        new PendingFuture<T>(_context, source, computeValue);
+    if (!pendingFuture.evaluate(sourceEntry)) {
+      _context._pendingFutureSources
+          .putIfAbsent(source, () => <PendingFuture>[])
+          .add(pendingFuture);
+    }
+    return pendingFuture.future;
+  }
+}