Fix MediaSource.duration setter behavior to match the current spec.

Source/modules/mediasource/MediaSource.h

 /*
  * 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 104 matching lines @@
 
     void setReadyState(const AtomicString&);
     void onReadyStateChange(const AtomicString&, const AtomicString&);
 
     bool isUpdating() const;
 
     PassOwnPtr<blink::WebSourceBuffer> createWebSourceBuffer(const String& type, const Vector<String>& codecs, ExceptionState&);
     void scheduleEvent(const AtomicString& eventName);
     void endOfStreamInternal(const blink::WebMediaSource::EndOfStreamStatus, ExceptionState&);
 
+    // Implements the duration change algorithm.
+    // https://dvcs.w3.org/hg/html-media/raw-file/default/media-source/media-source.html#duration-change-algorithm
+    void durationChangeAlgorithm(double newDuration);
+
     OwnPtr<blink::WebMediaSource> m_webMediaSource;
     AtomicString m_readyState;
     OwnPtrWillBeMember<GenericEventQueue> m_asyncEventQueue;
     // FIXME: oilpan: This should become a Member. For now, m_attachedElement will be cleared by the HTMLMediaElement destructor.
     HTMLMediaElement* m_attachedElement;
 
     RefPtrWillBeMember<SourceBufferList> m_sourceBuffers;
     RefPtrWillBeMember<SourceBufferList> m_activeSourceBuffers;
 };
 
 } // namespace WebCore
 
 #endif