Implement "potentially playing" for media elements per spec

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 466 matching lines @@
     Timer<HTMLMediaElement> m_progressEventTimer;
     Timer<HTMLMediaElement> m_playbackProgressTimer;
     Timer<HTMLMediaElement> m_audioTracksTimer;
     RefPtrWillBeMember<TimeRanges> m_playedTimeRanges;
     OwnPtrWillBeMember<GenericEventQueue> m_asyncEventQueue;
 
     double m_playbackRate;
     double m_defaultPlaybackRate;
     NetworkState m_networkState;
     ReadyState m_readyState;
-    ReadyState m_readyStateMaximum;
     KURL m_currentSrc;
 
     RefPtrWillBeMember<MediaError> m_error;
 
     double m_volume;
     double m_lastSeekTime;
 
     double m_previousProgressTime;
 
     // Cached duration to suppress duplicate events if duration unchanged.
@@ skipping 131 matching lines @@
 inline bool isHTMLMediaElement(const HTMLElement& element)
 {
     return isHTMLAudioElement(element) || isHTMLVideoElement(element);
 }
 
 DEFINE_HTMLELEMENT_TYPE_CASTS_WITH_FUNCTION(HTMLMediaElement);
 
 } // namespace blink
 
 #endif // HTMLMediaElement_h