Adding event delegation.

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 116 matching lines @@
    *
    *     MediaElement.pauseEvent.forTarget(document.body).listen(...);
    *
    * See also:
    *
    * [addEventListener](http://docs.webplatform.org/wiki/dom/methods/addEventListener)
    */
   Stream<T> forTarget(EventTarget e, {bool useCapture: false}) {
     return new _EventStream(e, _eventType, useCapture);
   }
+
+  /**
+   * Gets a single event [Stream] which is the combinations of event streams
+   * for this event for each target.
+   *
+   * See also:
+   *
+   * * [forTarget]
+   */
+  Stream<T> forTargets(List<EventTarget> targets, {bool useCapture: false}) {
+    // Clone so modifications to the list don't affect this.
+    targets = new List.from(targets);
+
+    // Keep track of subscriptions so we unsubscribe from all when the stream
+    // we return is unsubscribed.
+    var subscriptions = [];
+    var controller;
+    controller = new StreamController<T>(onSubscriptionStateChange: () {
+      if (controller.hasSubscribers) {
+        assert(subscriptions.isEmpty);
+        for (var target in targets) {
+          subscriptions.add(forTarget(target, useCapture: useCapture).listen(
+            (e) {
+              controller.add(e);
+            }));
+        }
+      } else {
+        assert(subscriptions.length == targets.length);
+        for (var subscription in subscriptions) {
+          subscription.cancel();
+        }
+        subscriptions.clear();
+      }
+    });
+    return controller.stream;
+  }
 }
 
 /**
  * A factory to expose DOM events as streams, where the DOM event name has to
  * be determined on the fly (for example, mouse wheel events).
  */
 class _CustomEventStreamProvider<T extends Event>
     implements EventStreamProvider<T> {
 
   final _eventTypeGetter;
   const _CustomEventStreamProvider(this._eventTypeGetter);
 
   Stream<T> forTarget(EventTarget e, {bool useCapture: false}) {
     return new _EventStream(e, _eventTypeGetter(e), useCapture);
   }
 }