Try to use incremental resolution after removing overlays.

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/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,
@@ skipping 251 matching lines @@
     importedLibraries = libAElement.importedLibraries;
     expect(importedLibraries, hasLength(1));
     return pumpEventQueue().then((_) {
       listener.assertEvent(wereSourcesAdded: true);
       listener.assertEvent(wereSourcesAdded: true);
       listener.assertEvent(wereSourcesRemovedOrDeleted: true);
       listener.assertNoMoreEvents();
     });
   }
 
+  /**
+   * IDEA uses the following scenarion:
+   * 1. Add overlay.
+   * 2. Change overlay.
+   * 3. If the contents of the document buffer is the same as the contents
+   *    of the file, remove overlay.
+   * So, we need to try to use incremental resolution for removing overlays too.
+   */
+  void test_applyChanges_remove_incremental() {
+    MemoryResourceProvider resourceProvider = new MemoryResourceProvider();
+    Source source = resourceProvider.newFile('/test.dart', r'''
+main() {
+  print(1);
+}
+''').createSource();
+    context.analysisOptions = new AnalysisOptionsImpl()..incremental = true;
+    context.applyChanges(new ChangeSet()..addedSource(source));
+    // remember compilation unit
+    _analyzeAll_assertFinished();
+    CompilationUnit unit = context.getResolvedCompilationUnit2(source, source);
+    // add overlay
+    context.setContents(source, r'''
+main() {
+  print(12);
+}
+''');
+    _analyzeAll_assertFinished();
+    expect(context.getResolvedCompilationUnit2(source, source), unit);
+    // remove overlay
+    context.setContents(source, null);
+    _analyzeAll_assertFinished();
+    expect(context.getResolvedCompilationUnit2(source, source), unit);
+  }
+
   Future test_applyChanges_removeContainer() {
     SourcesChangedListener listener = new SourcesChangedListener();
     context.onSourcesChanged.listen(listener.onData);
     String libAContents = r'''
 library libA;
 import 'libB.dart';''';
     Source libA = addSource("/libA.dart", libAContents);
     String libBContents = "library libB;";
     Source libB = addSource("/libB.dart", libBContents);
     context.computeLibraryElement(libA);
@@ skipping 1980 matching lines @@
   }
 }
 
 class _AnalysisContextImplTest_test_applyChanges_removeContainer
     implements SourceContainer {
   Source libB;
   _AnalysisContextImplTest_test_applyChanges_removeContainer(this.libB);
   @override
   bool contains(Source source) => source == libB;
 }