Fix type of EninePlugin List<ResultDescriptor> getters.

pkg/analyzer/lib/src/plugin/engine_plugin.dart

Index: pkg/analyzer/lib/src/plugin/engine_plugin.dart
diff --git a/pkg/analyzer/lib/src/plugin/engine_plugin.dart b/pkg/analyzer/lib/src/plugin/engine_plugin.dart
index 8f8a58f97270377d3376b8cc42c5263b39a555b0..e1f20e953ec00809742f9c35d71b5ce081d6ee02 100644
--- a/pkg/analyzer/lib/src/plugin/engine_plugin.dart
+++ b/pkg/analyzer/lib/src/plugin/engine_plugin.dart
@@ -100,7 +100,7 @@ class EnginePlugin implements Plugin {
    * descriptors for Dart sources.
    */
   @ExtensionPointId('DART_ERRORS_FOR_SOURCE_EXTENSION_POINT_ID')
-  List<TaskDescriptor> get dartErrorsForSource =>
+  List<ResultDescriptor> get dartErrorsForSource =>
       dartErrorsForSourceExtensionPoint.extensions;
 
   /**
@@ -108,7 +108,7 @@ class EnginePlugin implements Plugin {
    * descriptors for Dart library specific units.
    */
   @ExtensionPointId('DART_ERRORS_FOR_UNIT_EXTENSION_POINT_ID')
-  List<TaskDescriptor> get dartErrorsForUnit =>
+  List<ResultDescriptor> get dartErrorsForUnit =>
       dartErrorsForUnitExtensionPoint.extensions;
 
   /**
@@ -116,7 +116,7 @@ class EnginePlugin implements Plugin {
    * 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.