Add a dataTransfer member to MouseEvent

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 16c61a918ade302ea14a7f41834404d33c72660b..078f51b8cb5527bd063fea16bef051b3b2b5f36c 100644
--- a/sdk/lib/html/dart2js/html_dart2js.dart
+++ b/sdk/lib/html/dart2js/html_dart2js.dart
@@ -25381,6 +25381,10 @@ class MouseEvent extends UIEvent {
   @DomName('MouseEvent.pageX')
   @DomName('MouseEvent.pageY')
   Point get page => new Point/*<num>*/(_pageX, _pageY);
+
+  @DomName('MouseEvent.dataTransfer')
+  DataTransfer get dataTransfer =>
+      JS('DataTransfer', "#['dataTransfer']", this);
 }
 // 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