Remove many explicit references to AnalysisContextImpl and enable testing of the new task model

pkg/analysis_server/test/context_manager_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.context.directory.manager;
 
 import 'dart:collection';
 
 import 'package:analysis_server/src/context_manager.dart';
 import 'package:analysis_server/src/source/optimizing_pub_package_map_provider.dart';
@@ skipping 908 matching lines @@
 
 class TestContextManager extends ContextManager {
   /**
    * Source of timestamps stored in [currentContextFilePaths].
    */
   int now = 0;
 
   /**
    * The analysis context that was created.
    */
-  AnalysisContextImpl currentContext;
+  AnalysisContext currentContext;
 
   /**
    * Map from context to the timestamp when the context was created.
    */
   Map<String, int> currentContextTimestamps = <String, int>{};
 
   /**
    * Map from context to (map from file path to timestamp of last event).
    */
   final Map<String, Map<String, int>> currentContextFilePaths =
@@ skipping 23 matching lines @@
   Iterable<String> get currentContextPaths => currentContextTimestamps.keys;
 
   @override
   AnalysisContext addContext(Folder folder, UriResolver packageUriResolver) {
     String path = folder.path;
     expect(currentContextPaths, isNot(contains(path)));
     currentContextTimestamps[path] = now;
     currentContextFilePaths[path] = <String, int>{};
     currentContextSources[path] = new HashSet<Source>();
     currentContextPackageUriResolvers[path] = packageUriResolver;
-    currentContext = new AnalysisContextImpl();
+    currentContext = AnalysisEngine.instance.createAnalysisContext();
     currentContext.sourceFactory = new SourceFactory(
         packageUriResolver == null ? [] : [packageUriResolver]);
     return currentContext;
   }
 
   @override
   void applyChangesToContext(Folder contextFolder, ChangeSet changeSet) {
     Map<String, int> filePaths = currentContextFilePaths[contextFolder.path];
     Set<Source> sources = currentContextSources[contextFolder.path];
 
@@ skipping 47 matching lines @@
     // causing the analyzer to thrash, just ignore links to non-existent files.
     return file.exists;
   }
 
   @override
   void updateContextPackageUriResolver(
       Folder contextFolder, UriResolver packageUriResolver) {
     currentContextPackageUriResolvers[contextFolder.path] = packageUriResolver;
   }
 }