Fix MediaSource.duration setter behavior to match the current 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 131 matching lines @@
     void setLoop(bool b);
     void play();
     void pause();
 
     // statistics
     unsigned webkitAudioDecodedByteCount() const;
     unsigned webkitVideoDecodedByteCount() const;
 
     // media source extensions
     void closeMediaSource();
-    void durationChanged(double duration);
+    void durationChanged(double duration, bool requestSeek);
 
     // controls
     bool controls() const;
     void setControls(bool);
     double volume() const;
     void setVolume(double, ExceptionState&);
     bool muted() const;
     void setMuted(bool);
 
     // play/pause toggling that uses the media controller if present. togglePlayStateWillPlay() is
@@ skipping 176 matching lines @@
     virtual void mediaPlayerSetWebLayer(blink::WebLayer*) OVERRIDE FINAL;
     virtual void mediaPlayerMediaSourceOpened(blink::WebMediaSource*) OVERRIDE FINAL;
 
     void loadTimerFired(Timer<HTMLMediaElement>*);
     void progressEventTimerFired(Timer<HTMLMediaElement>*);
     void playbackProgressTimerFired(Timer<HTMLMediaElement>*);
     void startPlaybackProgressTimer();
     void startProgressEventTimer();
     void stopPeriodicTimers();
 
-    void seek(double time, ExceptionState&);
+    enum SeekSkipPermission { SkipAllowed, SkipNotAllowed};
+    void seek(SeekSkipPermission, double time, ExceptionState&);
     void finishSeek();
     void checkIfSeekNeeded();
     void addPlayedRange(double start, double end);
 
     void scheduleTimeupdateEvent(bool periodicEvent);
     void scheduleEvent(const AtomicString& eventName); // FIXME: Rename to scheduleNamedEvent for clarity.
 
     // loading
     void prepareForLoad();
     void loadInternal();
@@ skipping 199 matching lines @@
 inline bool isHTMLMediaElement(const HTMLElement& element)
 {
     return isHTMLAudioElement(element) || isHTMLVideoElement(element);
 }
 
 DEFINE_HTMLELEMENT_TYPE_CASTS_WITH_FUNCTION(HTMLMediaElement);
 
 } //namespace
 
 #endif