MediaSource must use ref-counting to handle pending activity counting.

Source/core/html/HTMLMediaElement.h

 /*
  * Copyright (C) 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 506 matching lines @@
     DeferredLoadState m_deferredLoadState;
     Timer<HTMLMediaElement> m_deferredLoadTimer;
 
     OwnPtr<MediaPlayer> m_player;
     blink::WebLayer* m_webLayer;
 
     MediaPlayer::Preload m_preload;
 
     DisplayMode m_displayMode;
 
-    RefPtr<HTMLMediaSource> m_mediaSource;
+    RefPtrWillBeMember<HTMLMediaSource> m_mediaSource;
 
     mutable double m_cachedTime;
     mutable double m_cachedTimeWallClockUpdateTime;
     mutable double m_minimumWallClockTimeToCacheMediaTime;
 
     double m_fragmentStartTime;
     double m_fragmentEndTime;
 
     typedef unsigned PendingActionFlags;
     PendingActionFlags m_pendingActionFlags;
@@ skipping 83 matching lines @@
 inline bool isHTMLMediaElement(const HTMLElement& element)
 {
     return isHTMLAudioElement(element) || isHTMLVideoElement(element);
 }
 
 DEFINE_HTMLELEMENT_TYPE_CASTS_WITH_FUNCTION(HTMLMediaElement);
 
 } //namespace
 
 #endif