Add a dataTransfer member to MouseEvent

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 0727fdd0acbd2239aafd92d6aabdd1771e899a25..48522d5129d806f3585c14cde22abec2aae7734f 100644
--- a/sdk/lib/html/dartium/html_dartium.dart
+++ b/sdk/lib/html/dartium/html_dartium.dart
@@ -28996,6 +28996,10 @@ 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.JsNative.getProperty(js.context, 'dataTransfer');
 }
 // 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