Allowing Window.onBeforeUnload event to work properly.

sdk/lib/html/dart2js/html_dart2js.dart

Index: sdk/lib/html/dart2js/html_dart2js.dart
diff --git a/sdk/lib/html/dart2js/html_dart2js.dart b/sdk/lib/html/dart2js/html_dart2js.dart
index 066b61e898bc065d122296463caa4fd7572edead..922ee8bb641cf3a57103862137bdf1e7864d4841 100644
--- a/sdk/lib/html/dart2js/html_dart2js.dart
+++ b/sdk/lib/html/dart2js/html_dart2js.dart
@@ -10436,7 +10436,7 @@ class Event native "*Event" {
 
   @DomName('Event.returnValue')
   @DocsEditable
-  bool returnValue;
+  Object returnValue;

[sra1, 2013/02/13 21:36:21]

This needs a @Creates annotation to indicate that reading it does not create
instances of all native types.
Use @Creates('Null'), that is what is used elsewhere.

 
   EventTarget get target => _convertNativeToDart_EventTarget(this._target);
   @JSName('target')
@@ -31088,7 +31088,7 @@ class _Device {
 // BSD-style license that can be found in the LICENSE file.
 
 
-typedef void EventListener(Event event);
+typedef EventListener(Event event);
 // 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.