Fix type of EninePlugin List<ResultDescriptor> getters.

pkg/analyzer/lib/src/plugin/engine_plugin.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 analyzer.src.plugin.engine_plugin;
 
 import 'package:analyzer/plugin/task.dart';
 import 'package:analyzer/src/generated/engine.dart'
     show InternalAnalysisContext;
 import 'package:analyzer/src/generated/error.dart' show AnalysisError;
@@ skipping 82 matching lines @@
   /**
    * Initialize a newly created plugin.
    */
   EnginePlugin();
 
   /**
    * Return a list containing all of the contributed analysis error result
    * descriptors for Dart sources.
    */
   @ExtensionPointId('DART_ERRORS_FOR_SOURCE_EXTENSION_POINT_ID')
-  List<TaskDescriptor> get dartErrorsForSource =>
+  List<ResultDescriptor> get dartErrorsForSource =>
       dartErrorsForSourceExtensionPoint.extensions;
 
   /**
    * Return a list containing all of the contributed analysis error result
    * descriptors for Dart library specific units.
    */
   @ExtensionPointId('DART_ERRORS_FOR_UNIT_EXTENSION_POINT_ID')
-  List<TaskDescriptor> get dartErrorsForUnit =>
+  List<ResultDescriptor> get dartErrorsForUnit =>
       dartErrorsForUnitExtensionPoint.extensions;
 
   /**
    * Return a list containing all of the contributed analysis error result
    * descriptors for HTML sources.
    */
   @ExtensionPointId('HTML_ERRORS_EXTENSION_POINT_ID')
-  List<TaskDescriptor> get htmlErrors => htmlErrorsExtensionPoint.extensions;
+  List<ResultDescriptor> get htmlErrors => htmlErrorsExtensionPoint.extensions;
 
   /**
    * Return a list containing all of the task descriptors that were contributed.
    */
   List<TaskDescriptor> get taskDescriptors => taskExtensionPoint.extensions;
 
   @override
   String get uniqueIdentifier => UNIQUE_IDENTIFIER;
 
   /**
@@ skipping 148 matching lines @@
  * passed to the extension manager to populate it.
  *
  * This annotation is not used at runtime; it is used to aid in static analysis
  * of the task model during development.
  */
 class ExtensionPointId {
   final String extensionPointId;
 
   const ExtensionPointId(this.extensionPointId);
 }