Use contributed ResultDescriptor(s) while computing DART_ERRORS.

pkg/analyzer/lib/plugin/task.dart

Index: pkg/analyzer/lib/plugin/task.dart
diff --git a/pkg/analyzer/lib/plugin/task.dart b/pkg/analyzer/lib/plugin/task.dart
index 72c33fa78fc7f68334011a2b1764a0357ace0a7d..45141a2e8836ef267fed0a01f1450993e0cb3d35 100644
--- a/pkg/analyzer/lib/plugin/task.dart
+++ b/pkg/analyzer/lib/plugin/task.dart
@@ -15,6 +15,24 @@ import 'package:plugin/plugin.dart';
 
 /**
  * The identifier of the extension point that allows plugins to register new
+ * analysis error results to compute for a Dart source. The object used as an
+ * extension must be a [ResultDescriptor].
+ */
+final String DART_ERRORS_FOR_SOURCE_EXTENSION_POINT_ID = Plugin.join(
+    EnginePlugin.UNIQUE_IDENTIFIER,
+    EnginePlugin.DART_ERRORS_FOR_SOURCE_EXTENSION_POINT);
+
+/**
+ * The identifier of the extension point that allows plugins to register new
+ * analysis error results to compute for a Dart library specific unit. The
+ * object used as an extension must be a [ResultDescriptor].
+ */
+final String DART_ERRORS_FOR_UNIT_EXTENSION_POINT_ID = Plugin.join(
+    EnginePlugin.UNIQUE_IDENTIFIER,
+    EnginePlugin.DART_ERRORS_FOR_UNIT_EXTENSION_POINT);
+
+/**
+ * The identifier of the extension point that allows plugins to register new
  * analysis tasks with the analysis engine. The object used as an extension must
  * be a [TaskDescriptor].
  */