Fix test failures on the bots

pkg/analyzer/test/src/context/abstract_context.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 test.src.task.abstract_context_test;
 
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer/src/context/cache.dart';
 import 'package:analyzer/src/context/context.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/engine.dart'
     hide AnalysisCache, AnalysisContextImpl, AnalysisTask;
 import 'package:analyzer/src/generated/sdk.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/task/driver.dart';
 import 'package:analyzer/task/model.dart';
+import 'package:plugin/manager.dart';
 import 'package:unittest/unittest.dart';
 
 import 'mock_sdk.dart';
 
 class AbstractContextTest {
   MemoryResourceProvider resourceProvider = new MemoryResourceProvider();
 
   DartSdk sdk = new MockSdk();
   SourceFactory sourceFactory;
   AnalysisContextImpl context;
@@ skipping 89 matching lines @@
     context = createAnalysisContext();
     if (options != null) {
       context.analysisOptions = options;
     }
     context.sourceFactory = sourceFactory;
     analysisCache = context.analysisCache;
     analysisDriver = context.driver;
   }
 
   void setUp() {
+    ExtensionManager extensionManager = new ExtensionManager();
+    extensionManager.processPlugins(AnalysisEngine.instance.supportedPlugins);
     prepareAnalysisContext();
   }
 
   void tearDown() {}
 }