Create pkg/front_end/src/base and begin populating with general use classes.

pkg/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 analyzer.src.generated.engine;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 11 matching lines @@
 import 'package:analyzer/src/generated/java_engine.dart';
 import 'package:analyzer/src/generated/resolver.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/generated/utilities_general.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/task/manager.dart';
 import 'package:analyzer/task/dart.dart';
 import 'package:analyzer/task/model.dart';
+import 'package:front_end/src/base/timestamped_data.dart';
 import 'package:html/dom.dart' show Document;
 import 'package:path/path.dart' as pathos;
 import 'package:plugin/manager.dart';
 import 'package:plugin/plugin.dart';
 
 export 'package:analyzer/error/listener.dart' show RecordingErrorListener;
+export 'package:front_end/src/base/timestamped_data.dart' show TimestampedData;
 
 /**
  * Used by [AnalysisOptions] to allow function bodies to be analyzed in some
  * sources but not others.
  */
 typedef bool AnalyzeFunctionBodiesPredicate(Source source);
 
 /**
  * A context in which a single analysis can be performed and incrementally
  * maintained. The context includes such information as the version of the SDK
@@ skipping 2665 matching lines @@
    */
   bool get wereSourcesAdded => _changeSet.addedSources.length > 0;
 
   /**
    * Return `true` if any sources were removed or deleted.
    */
   bool get wereSourcesRemoved =>
       _changeSet.removedSources.length > 0 ||
       _changeSet.removedContainers.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);
-}