Fixing wheel event on Dart2js

tools/dom/templates/html/impl/impl_WheelEvent.darttemplate

 // 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
 // BSD-style license that can be found in the LICENSE file.
 
 part of $LIBRARYNAME;
 
 $(ANNOTATIONS)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
 
   factory WheelEvent(String type,
       {Window view, int deltaX: 0, int deltaY: 0,
@@ skipping 46 matching lines @@
         detail = deltaY;
         axis = JS('int', 'MouseScrollEvent.VERTICAL_AXIS');
       } else if (deltaX != 0) {
         detail = deltaX;
         axis = JS('int', 'MouseScrollEvent.HORIZONTAL_AXIS');
       }
       event._initMouseScrollEvent(type, canBubble, cancelable, view, detail,
           screenX, screenY, clientX, clientY, ctrlKey, altKey, shiftKey,
           metaKey, button, relatedTarget, axis);
     } else {
+      // Chrome does an auto-convert to pixels.
+      deltaY = deltaY ~/ 120;
 $else
     // Dartium always needs these flipped because we're using the legacy
     // _initWebKitWheelEvent instead of the more modern WheelEvent constructor
     // which isn't yet properly exposed by the Dartium bindings.
     deltaX = -deltaX;
     deltaY = -deltaY;
 $endif
       // Fallthrough for Dartium.
       event._initMouseEvent(type, canBubble, cancelable, view, detail,
           screenX, screenY, clientX, clientY, ctrlKey, altKey, shiftKey,
@@ skipping 158 matching lines @@
    * [deltaMode].
    *
    * See also:
    *
    * * [WheelEvent.deltaY](http://dev.w3.org/2006/webapi/DOM-Level-3-Events/html/DOM3-Events.html#events-WheelEvent-deltaY) from the W3C.
    */
   @DomName('WheelEvent.deltaY')
   num get deltaY => _deltaY;
 $endif
 }