Improvements to task model

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/task/model.dart';
 
 class TestAnalysisTask extends AnalysisTask {
-  TestAnalysisTask(AnalysisContext context, AnalysisTarget target) : super(context, target);
+  TestAnalysisTask(AnalysisContext context, AnalysisTarget target)
+      : super(context, target);
 
   @override
   String get description => 'Test task';
 
   @override
+  TaskDescriptor get descriptor => null;
+
+  @override
   internalPerform() {
   }
 }