for discussion: support for zones in DOM events

tools/dom/src/EventStreamProvider.dart

 // Copyright (c) 2013, 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 html;
 
 /**
  * Adapter for exposing DOM events as Dart streams.
  */
 class _EventStream<T extends Event> extends Stream<T> {
@@ skipping 136 matching lines @@
   }
 }
 
 class _EventStreamSubscription<T extends Event> extends StreamSubscription<T> {
   int _pauseCount = 0;
   EventTarget _target;
   final String _eventType;
   var _onData;
   final bool _useCapture;
 
-  _EventStreamSubscription(this._target, this._eventType, this._onData,
-      this._useCapture) {
+  _EventStreamSubscription(this._target, this._eventType, onData,
+      this._useCapture) : _onData = _wrapZone(onData) {
     _tryResume();
   }
 
+  static _wrapZone(callback) {
+    // For performance reasons, avoid wrapping if we are in the default zone.
+    final zone = currentZoneExperimental;
+    if (zone.isDefault) return callback;
+
+    zone.expectCallback();
+    return (e) => zone.executePeriodicCallbackGuarded(() => callback(e));
+  }
+
   void cancel() {
     if (_canceled) return;
 
     _unlisten();
     // Clear out the target to indicate this is complete.
     _target = null;
     _onData = null;
+
+    final zone = currentZoneExperimental;
+    if (!zone.isDefault) zone.cancelCallbackExpectation();
   }
 
   bool get _canceled => _target == null;
 
   void onData(void handleData(T event)) {
     if (_canceled) {
       throw new StateError("Subscription has been canceled.");
     }
     // Remove current event listener.
     _unlisten();
 
-    _onData = handleData;
+    _onData = _wrapZone(handleData);
     _tryResume();
   }
 
   /// Has no effect.
   void onError(void handleError(error)) {}
 
   /// Has no effect.
   void onDone(void handleDone()) {}
 
   void pause([Future resumeSignal]) {
@@ skipping 130 matching lines @@
 
   ElementStream<T> _forElementList(ElementList e,
       {bool useCapture: false}) {
     return new _ElementListEventStreamImpl(e, _eventTypeGetter(e), useCapture);
   }
 
   String getEventType(EventTarget target) {
     return _eventTypeGetter(target);
   }
 }