Try to use incremental resolution after removing overlays.

pkg/analyzer/test/src/context/context_test.dart

Index: pkg/analyzer/test/src/context/context_test.dart
diff --git a/pkg/analyzer/test/src/context/context_test.dart b/pkg/analyzer/test/src/context/context_test.dart
index af84f24c6b3a9bbd4e66eecb185f0b5780f50e23..37c5939f1001f3dfcbfcf73e429adc2a315feaf1 100644
--- a/pkg/analyzer/test/src/context/context_test.dart
+++ b/pkg/analyzer/test/src/context/context_test.dart
@@ -6,6 +6,7 @@ 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';
@@ -277,6 +278,40 @@ import 'libB.dart';''';
     });
   }
 
+  /**
+   * 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);