Enable round-tripping and updating of SourceBuffer timestamp offset

Source/modules/mediasource/SourceBuffer.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 87 matching lines @@
     virtual const AtomicString& interfaceName() const OVERRIDE;
 
     void trace(Visitor*);
 
 private:
     SourceBuffer(PassOwnPtr<blink::WebSourceBuffer>, MediaSource*, GenericEventQueue*);
 
     bool isRemoved() const;
     void scheduleEvent(const AtomicString& eventName);
 
+    // Coded frame processing during append may update timestamp offset. This helper
+    // does the append, then remembers the new offset only if it was updated by the append.
+    void appendAndUpdateTimestampOffset(const unsigned char* data, unsigned length);
+
     void appendBufferInternal(const unsigned char*, unsigned, ExceptionState&);
     void appendBufferAsyncPart();
 
     void removeAsyncPart();
 
     void appendStreamInternal(PassRefPtr<Stream>, ExceptionState&);
     void appendStreamAsyncPart();
     void appendStreamDone(bool success);
     void clearAppendStreamState();
 
@@ skipping 23 matching lines @@
     bool m_streamMaxSizeValid;
     unsigned long long m_streamMaxSize;
     AsyncMethodRunner<SourceBuffer> m_appendStreamAsyncPartRunner;
     RefPtr<Stream> m_stream;
     OwnPtr<FileReaderLoader> m_loader;
 };
 
 } // namespace WebCore
 
 #endif