Add an option to enable the new task model

pkg/analyzer/lib/src/generated/engine.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;
 
 import "dart:math" as math;
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analyzer/src/cancelable_future.dart';
 import 'package:analyzer/src/context/cache.dart' as cache;
-import 'package:analyzer/src/context/context.dart' as cache;
+import 'package:analyzer/src/context/context.dart' as newContext;
 import 'package:analyzer/src/generated/incremental_resolution_validator.dart';
 import 'package:analyzer/src/plugin/engine_plugin.dart';
 import 'package:analyzer/src/services/lint.dart';
 import 'package:analyzer/src/task/manager.dart';
 import 'package:analyzer/src/task/task_dart.dart';
 import 'package:analyzer/task/model.dart';
 
 import '../../instrumentation/instrumentation.dart';
 import 'ast.dart';
 import 'constant.dart';
@@ skipping 5732 matching lines @@
       InstrumentationService.NULL_SERVICE;
 
   /**
    * The partition manager being used to manage the shared partitions.
    */
   final PartitionManager partitionManager = new PartitionManager();
 
   /**
    * The partition manager being used to manage the shared partitions.
    */
-  final cache.PartitionManager partitionManager_new =
-      new cache.PartitionManager();
+  final newContext.PartitionManager partitionManager_new =
+      new newContext.PartitionManager();
 
   /**
    * A flag indicating whether the (new) task model should be used to perform
    * analysis.
    */
   bool useTaskModel = false;
 
   /**
    * The task manager used to manage the tasks used to analyze code.
    */
@@ skipping 49 matching lines @@
    * will be performed the next time an analysis context is created.
    */
   void clearCaches() {
     partitionManager.clearCache();
   }
 
   /**
    * Create and return a new context in which analysis can be performed.
    */
   AnalysisContext createAnalysisContext() {
+    if (useTaskModel) {
+      return new newContext.AnalysisContextImpl();
+    }
     return new AnalysisContextImpl();
   }
 
   /**
    * Return `true` if the given [fileName] is assumed to contain Dart source
    * code.
    */
   static bool isDartFileName(String fileName) {
     if (fileName == null) {
       return false;
@@ skipping 5886 matching lines @@
   visitElement(Element element) {
     if (element.id == _id) {
       result = element;
       throw new _ElementByIdFinderException();
     }
     super.visitElement(element);
   }
 }
 
 class _ElementByIdFinderException {}