More minor type improvements in dart:async.

sdk/lib/async/stream_controller.dart

 // Copyright (c) 2012, 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.
 
 part of dart.async;
 
 // -------------------------------------------------------------------
 // Controller for creating and adding events to a stream.
 // -------------------------------------------------------------------
 
@@ skipping 774 matching lines @@
 // constructors in mixin superclasses.
 
 class _AsyncStreamController<T> = _StreamController<T>
     with _AsyncStreamControllerDispatch<T>;
 
 class _SyncStreamController<T> = _StreamController<T>
     with _SyncStreamControllerDispatch<T>;
 
 typedef _NotificationHandler();
 
-Future _runGuarded(_NotificationHandler notificationHandler) {
-  if (notificationHandler == null) return null;
+void _runGuarded(_NotificationHandler notificationHandler) {
+  if (notificationHandler == null) return;
   try {
-    var result = notificationHandler();
-    if (result is Future) return result;
-    return null;
+    notificationHandler();
   } catch (e, s) {
     Zone.current.handleUncaughtError(e, s);
   }
 }
 
 class _ControllerStream<T> extends _StreamImpl<T> {
   _StreamControllerLifecycle<T> _controller;
 
   _ControllerStream(this._controller);
 
@@ skipping 116 matching lines @@
   var varData;
 
   _StreamControllerAddStreamState(_StreamController<T> controller, this.varData,
       Stream source, bool cancelOnError)
       : super(controller, source, cancelOnError) {
     if (controller.isPaused) {
       addSubscription.pause();
     }
   }
 }