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

pkg/analyzer/test/src/task/test_support.dart

Index: pkg/analyzer/test/src/task/test_support.dart
diff --git a/pkg/analyzer/test/src/task/test_support.dart b/pkg/analyzer/test/src/task/test_support.dart
index 80cd7c3a4a2610ac88775644a04fa1d6816559af..7ac0d82266eac6ced9b47d30cb368575cc809449 100644
--- a/pkg/analyzer/test/src/task/test_support.dart
+++ b/pkg/analyzer/test/src/task/test_support.dart
@@ -23,6 +23,11 @@ class TestAnalysisTask extends AnalysisTask {
   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;
@@ -33,7 +38,8 @@ class TestAnalysisTask extends AnalysisTask {
   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
@@ -47,10 +53,12 @@ class TestAnalysisTask extends AnalysisTask {
       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;
     }
   }
 }