Have DOMWindow deal with references instead of pointers when possible

Source/modules/mediasource/VideoPlaybackQuality.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 32 matching lines @@
     return adoptRefWillBeNoop(new VideoPlaybackQuality(document, totalVideoFrames, droppedVideoFrames, corruptedVideoFrames));
 }
 
 VideoPlaybackQuality::VideoPlaybackQuality(
     const Document& document, unsigned totalVideoFrames, unsigned droppedVideoFrames, unsigned corruptedVideoFrames)
     : m_creationTime(0)
     , m_totalVideoFrames(totalVideoFrames)
     , m_droppedVideoFrames(droppedVideoFrames)
     , m_corruptedVideoFrames(corruptedVideoFrames)
 {
-    if (document.domWindow() && document.domWindow()->performance())
-        m_creationTime = document.domWindow()->performance()->now();
+    if (document.domWindow())
+        m_creationTime = document.domWindow()->performance().now();
 }
 
 }