Get memento objects from tasks, remember in cache and pass back to tasks.

pkg/analyzer/test/src/task/test_support.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.test_support;
 
 import 'package:analyzer/src/generated/engine.dart' hide AnalysisTask;
 import 'package:analyzer/src/generated/java_engine.dart';
 import 'package:analyzer/task/model.dart';
 
 /**
  * A configurable analysis task that can be used by tests.
  */
 class TestAnalysisTask extends AnalysisTask {
   /**
    * The descriptor describing this task.
    */
   TaskDescriptor descriptor;
 
   /**
    * The exception that is to be "thrown" by this task.
    */
   CaughtException exception;
 
   /**
+   * The memento to associate with the result.
+   */
+  dynamic memento;
+
+  /**
    * The results whose values are to be provided as outputs from this task.
    */
   List<ResultDescriptor> results;
 
   /**
    * The next value that is to be used for a result.
    */
   int value;
 
   TestAnalysisTask(AnalysisContext context, AnalysisTarget target,
-      {this.descriptor, this.exception, this.results, this.value: 1})
+      {this.descriptor, this.exception, this.memento, this.results,
+      this.value: 1})
       : super(context, target);
 
   @override
   String get description => 'Test task';
 
   @override
   internalPerform() {
     if (exception != null) {
       caughtException = exception;
     } else if (results != null) {
       for (ResultDescriptor result in results) {
         outputs[result] = value++;
       }
+      outputMemento = memento;
     } else if (descriptor != null) {
       for (ResultDescriptor result in descriptor.results) {
         outputs[result] = value++;
       }
+      outputMemento = memento;
     }
   }
 }