Fix incremental kernel builder to handle multiple calls to computeDelta.

pkg/front_end/lib/src/incremental_resolved_ast_generator_impl.dart

 // Copyright (c) 2017, 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.
 
 import 'dart:async';
 
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/src/context/context.dart';
 import 'package:analyzer/src/dart/analysis/byte_store.dart';
 import 'package:analyzer/src/dart/analysis/driver.dart' as driver;
@@ skipping 33 matching lines @@
     implements IncrementalResolvedAstGenerator {
   driver.AnalysisDriverScheduler _scheduler;
   final _pathToUriMap = <String, Uri>{};
   final _uriToPathMap = <Uri, String>{};
   final _fileContents = <String, String>{};
   _ResourceProviderProxy _resourceProvider;
   driver.AnalysisDriver _driver;
   bool _isInitialized = false;
   final ProcessedOptions _options;
   final Uri _source;
+  bool _schedulerStarted = false;
 
   IncrementalResolvedAstGeneratorImpl(this._source, this._options);
 
   @override
   Future<DeltaLibraries> computeDelta() async {
     if (!_isInitialized) {
       await init();
     }
     // The analysis driver doesn't currently support an asynchronous file API,
     // so we have to find all the files first to read their contents.
     // TODO(paulberry): this is an unnecessary source of duplicate work and
     // should be eliminated ASAP.
     var graph = await graphForProgram([_source], _options);
     var libraries = <Uri, ResolvedLibrary>{};
     // TODO(paulberry): it should be possible to seed the driver using a URI,
     // not a file path.
-    // TODO(paulberry): only start the scheduler the first time.
-    _scheduler.start();
+    if (!_schedulerStarted) {
+      _scheduler.start();
+      _schedulerStarted = true;
+    }
     _driver.addFile(_source.path);
     for (var libraryCycle in graph.topologicallySortedCycles) {
       for (var uri in libraryCycle.libraries.keys) {
         var contents =
             await _options.fileSystem.entityForUri(uri).readAsString();
         _storeVirtualFile(uri, uri.path, contents);
       }
       // The driver will request files from dart:, even though it actually uses
       // the data from the summary.  TODO(paulberry): fix this.
       _storeVirtualFile(_DartSdkProxy._dartCoreSource.uri, 'core.dart', '');
@@ skipping 41 matching lines @@
     _isInitialized = true;
   }
 
   @override
   void invalidate(String path) {
     throw new UnimplementedError();
   }
 
   @override
   void invalidateAll() {
-    throw new UnimplementedError();
+    // TODO(paulberry): verify that this has an effect (requires a multi-file
+    // test).
+    if (_isInitialized) {
+      _driver.knownFiles.forEach(_driver.changeFile);
+    }
   }
 
   void _storeVirtualFile(Uri uri, String path, String contents) {
     _pathToUriMap[path] = uri;
     _uriToPathMap[uri] = path;
     _fileContents[path] = contents;
   }
 }
 
 class _DartSdkProxy implements DartSdk {
@@ skipping 94 matching lines @@
   final Map<String, Uri> pathToUriMap;
 
   final Map<Uri, String> uriToPathMap;
 
   @override
   AnalysisContext context;
 
   _SourceFactoryProxy(this.dartSdk, this.pathToUriMap, this.uriToPathMap);
 
   @override
-  SourceFactory clone() => this;
+  SourceFactory clone() =>
+      new _SourceFactoryProxy(dartSdk, pathToUriMap, uriToPathMap);
 
   @override
   Source forUri(String absoluteUri) {
     if (absoluteUri == 'dart:core') return _DartSdkProxy._dartCoreSource;
     Uri uri = Uri.parse(absoluteUri);
     assert(uriToPathMap.containsKey(uri));
     return new _SourceProxy(uri, uriToPathMap[uri]);
   }
 
   noSuchMethod(Invocation invocation) => unimplemented();
@@ skipping 12 matching lines @@
 class _SourceProxy extends BasicSource {
   @override
   final String fullName;
 
   _SourceProxy(Uri uri, this.fullName) : super(uri);
 
   int get modificationStamp => 0;
 
   noSuchMethod(Invocation invocation) => unimplemented();
 }