Add an analysis option to disable cache flushing.

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

 // Copyright (c) 2015, 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 analyzer.test.src.context.cache_test;
 
 import 'package:analyzer/exception/exception.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer/file_system/physical_file_system.dart';
@@ skipping 1269 matching lines @@
     // dispose
     partition2.dispose();
     expect(partition1.get(target1), same(entry1));
     expect(partition2.get(target2), isNull);
     // result2 is removed from result1
     expect(entry1.getResultData(descriptor1).dependentResults, isEmpty);
   }
 }
 
 class _InternalAnalysisContextMock extends TypedMock
-    implements InternalAnalysisContext {}
+    implements InternalAnalysisContext {
+  @override
+  final AnalysisOptions analysisOptions = new AnalysisOptionsImpl();
+}
 
 /**
  * Keep the given [keepDescriptor], invalidate all the other results.
  */
 class _KeepContinueDelta implements Delta {
   final Source source;
   final ResultDescriptor keepDescriptor;
 
   _KeepContinueDelta(this.source, this.keepDescriptor);
 
@@ skipping 17 matching lines @@
     }
     return DeltaResult.INVALIDATE;
   }
 }
 
 class _TestAnalysisTarget implements AnalysisTarget {
   final Source librarySource;
   final Source source;
   _TestAnalysisTarget({this.librarySource, this.source});
 }