Revert "Change the way tasks are registered" (TBD)

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 a9059af473381f9bba98f411a9ae9a1114ff9d43..2a242de53efd002ef26c3dbc403b6bd81502da83 100644
--- a/pkg/analyzer/lib/plugin/task.dart
+++ b/pkg/analyzer/lib/plugin/task.dart
@@ -41,6 +41,20 @@ final String HTML_ERRORS_EXTENSION_POINT_ID = Plugin.join(
 
 /**
  * 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].
+ *
+ * Contributed tasks should never extract information from Dart elements or AST
+ * (e.g. offsets) of a source and put it into results for targets in other
+ * sources. Dart elements and ASTs are updated during incremental resolution,
+ * and invalidation of results is intentionally limited by the source bounds
+ * for performance reasons.
+ */
+final String TASK_EXTENSION_POINT_ID = Plugin.join(
+    EnginePlugin.UNIQUE_IDENTIFIER, EnginePlugin.TASK_EXTENSION_POINT);
+
+/**
+ * The identifier of the extension point that allows plugins to register new
  * work managers with the analysis engine. The object used as an extension must
  * be a [WorkManagerFactory].
  */