Fixing the BeforeUnloadEvent

sdk/lib/html/dartium/html_dartium.dart

Index: sdk/lib/html/dartium/html_dartium.dart
diff --git a/sdk/lib/html/dartium/html_dartium.dart b/sdk/lib/html/dartium/html_dartium.dart
index 302dad684f31a437f8132f26f2b5f713bf372957..5681bb058bd90458876dbd9ef938cf28a649ee0c 100644
--- a/sdk/lib/html/dartium/html_dartium.dart
+++ b/sdk/lib/html/dartium/html_dartium.dart
@@ -753,11 +753,18 @@ class BeforeLoadEvent extends Event {
 
 @DocsEditable()
 @DomName('BeforeUnloadEvent')
-@Experimental() // untriaged
 class BeforeUnloadEvent extends Event {
   // To suppress missing implicit constructor warnings.
   factory BeforeUnloadEvent._() { throw new UnsupportedError("Not supported"); }
 
+  @DomName('BeforeUnloadEvent.returnValue')
+  @DocsEditable()
+  String get returnValue native "BeforeUnloadEvent_returnValue_Getter";
+
+  @DomName('BeforeUnloadEvent.returnValue')
+  @DocsEditable()
+  void set returnValue(String value) native "BeforeUnloadEvent_returnValue_Setter";
+
 }
 // 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
@@ -25605,13 +25612,13 @@ class Url extends NativeFieldWrapperClass2 {
     if ((blob_OR_source_OR_stream is Blob || blob_OR_source_OR_stream == null)) {
       return _createObjectURL_1(blob_OR_source_OR_stream);
     }
-    if ((blob_OR_source_OR_stream is MediaSource || blob_OR_source_OR_stream == null)) {
+    if ((blob_OR_source_OR_stream is MediaStream || blob_OR_source_OR_stream == null)) {
       return _createObjectURL_2(blob_OR_source_OR_stream);
     }
-    if ((blob_OR_source_OR_stream is _WebKitMediaSource || blob_OR_source_OR_stream == null)) {
+    if ((blob_OR_source_OR_stream is MediaSource || blob_OR_source_OR_stream == null)) {
       return _createObjectURL_3(blob_OR_source_OR_stream);
     }
-    if ((blob_OR_source_OR_stream is MediaStream || blob_OR_source_OR_stream == null)) {
+    if ((blob_OR_source_OR_stream is _WebKitMediaSource || blob_OR_source_OR_stream == null)) {
       return _createObjectURL_4(blob_OR_source_OR_stream);
     }
     throw new ArgumentError("Incorrect number or type of arguments");
@@ -27028,17 +27035,6 @@ class Window extends EventTarget implements WindowBase, _WindowTimers, WindowBas
 
 }
 
-class _BeforeUnloadEvent extends _WrappedEvent implements BeforeUnloadEvent {
-  String _returnValue;
-
-  _BeforeUnloadEvent(Event base): super(base);
-
-  String get returnValue => _returnValue;
-
-  void set returnValue(String value) {
-    _returnValue = value;
-  }
-}
 
 class _BeforeUnloadEventStreamProvider implements
     EventStreamProvider<BeforeUnloadEvent> {
@@ -27047,15 +27043,8 @@ class _BeforeUnloadEventStreamProvider implements
   const _BeforeUnloadEventStreamProvider(this._eventType);
 
   Stream<BeforeUnloadEvent> forTarget(EventTarget e, {bool useCapture: false}) {
-    var controller = new StreamController(sync: true);
     var stream = new _EventStream(e, _eventType, useCapture);
-    stream.listen((event) {
-      var wrapped = new _BeforeUnloadEvent(event);
-      controller.add(wrapped);
-      return wrapped.returnValue;
-    });
-
-    return controller.stream;
+    return stream;
   }
 
   String getEventType(EventTarget target) {