Screen Orientation: fire event on Window instead of Screen.

Source/modules/screen_orientation/ScreenOrientation.idl

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 enum OrientationType {
     "portrait-primary",
     "portrait-secondary",
     "landscape-primary",
     "landscape-secondary"
 };
 
 enum OrientationLockType {
     "any",
     "landscape",
     "portrait",
     "portrait-primary",
     "portrait-secondary",
     "landscape-primary",
     "landscape-secondary"
 };
 
 [
     RuntimeEnabled=ScreenOrientation
 ] partial interface Screen {
     readonly attribute OrientationType orientation;
 
     boolean lockOrientation(OrientationLockType orientation);
 
     void unlockOrientation();
-    attribute EventHandler onorientationchange;
 };