Add ApplyChangesStatus to AnalysisContext.applyChanges() and use it in DAS.

pkg/analyzer/test/src/context/context_test.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 test.src.context.context_test;
 
 import 'dart:async';
 
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer/source/package_map_resolver.dart';
 import 'package:analyzer/src/cancelable_future.dart';
 import 'package:analyzer/src/context/cache.dart';
 import 'package:analyzer/src/context/context.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/engine.dart'
     show
         AnalysisContext,
         AnalysisContextStatistics,
         AnalysisDelta,
         AnalysisEngine,
         AnalysisErrorInfo,
         AnalysisLevel,
         AnalysisNotScheduledError,
         AnalysisOptions,
         AnalysisOptionsImpl,
         AnalysisResult,
+        ApplyChangesStatus,
         CacheState,
         ChangeNotice,
         ChangeSet,
         IncrementalAnalysisCache,
         TimestampedData;
 import 'package:analyzer/src/generated/error.dart';
 import 'package:analyzer/src/generated/java_engine.dart';
 import 'package:analyzer/src/generated/resolver.dart';
 import 'package:analyzer/src/generated/scanner.dart';
 import 'package:analyzer/src/generated/source.dart';
@@ skipping 251 matching lines @@
       listener.assertNoMoreEvents();
     });
   }
 
   void test_applyChanges_empty() {
     context.applyChanges(new ChangeSet());
     expect(context.performAnalysisTask().changeNotices, isNull);
   }
 
   void test_applyChanges_overriddenSource() {
-    // Note: addSource adds the source to the contentCache.
-    Source source = addSource("/test.dart", "library test;");
+    String content = "library test;";
+    Source source = addSource("/test.dart", content);
+    context.setContents(source, content);
     context.computeErrors(source);
     while (!context.sourcesNeedingProcessing.isEmpty) {
       context.performAnalysisTask();
     }
     // Adding the source as a changedSource should have no effect since
     // it is already overridden in the content cache.
     ChangeSet changeSet = new ChangeSet();
     changeSet.changedSource(source);
-    context.applyChanges(changeSet);
+    ApplyChangesStatus changesStatus = context.applyChanges(changeSet);
+    expect(changesStatus.hasChanges, isFalse);
     expect(context.sourcesNeedingProcessing, hasLength(0));
   }
 
   Future test_applyChanges_remove() {
     SourcesChangedListener listener = new SourcesChangedListener();
     context.onSourcesChanged.listen(listener.onData);
     String libAContents = r'''
 library libA;
 import 'libB.dart';''';
     Source libA = addSource("/libA.dart", libAContents);
@@ skipping 2404 matching lines @@
   }
 }
 
 class _AnalysisContextImplTest_test_applyChanges_removeContainer
     implements SourceContainer {
   Source libB;
   _AnalysisContextImplTest_test_applyChanges_removeContainer(this.libB);
   @override
   bool contains(Source source) => source == libB;
 }