One more fix for making removing overlays incremental changes.

pkg/analyzer/test/generated/engine_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.
 
 // This code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 
 library engine.engine_test;
 
 import 'dart:async';
@@ skipping 461 matching lines @@
     // add overlay
     _context.setContents(source, r'''
 main() {
   print(12);
 }
 ''');
     _analyzeAll_assertFinished();
     expect(_context.getResolvedCompilationUnit2(source, source), unit);
     // remove overlay
     _context.setContents(source, null);
+    _context.validateCacheConsistency();
     _analyzeAll_assertFinished();
     expect(_context.getResolvedCompilationUnit2(source, source), unit);
   }
 
   Future test_applyChanges_removeContainer() {
     _context = AnalysisContextFactory.oldContextWithCore();
     SourcesChangedListener listener = new SourcesChangedListener();
     _context.onSourcesChanged.listen(listener.onData);
     _sourceFactory = _context.sourceFactory;
     String libAContents = r'''
@@ skipping 6172 matching lines @@
   @override
   bool exists() => true;
 }
 
 class _UniversalCachePartitionTest_test_setMaxCacheSize
     implements CacheRetentionPolicy {
   @override
   RetentionPriority getAstPriority(Source source, SourceEntry sourceEntry) =>
       RetentionPriority.LOW;
 }