Initialize media timeline correctly for positive start times.

media/base/demuxer.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MEDIA_BASE_DEMUXER_H_
 #define MEDIA_BASE_DEMUXER_H_
 
 #include <vector>
 
 #include "base/time/time.h"
@@ skipping 55 matching lines @@
   // callback upon completion.
   virtual void Seek(base::TimeDelta time,
                     const PipelineStatusCB& status_cb) = 0;
 
   // Stops this demuxer.
   //
   // After this call the demuxer may be destroyed. It is illegal to call any
   // method (including Stop()) after a demuxer has stopped.
   virtual void Stop() = 0;
 
+  // Returns the starting time for the media file; it's always positive.
+  virtual base::TimeDelta GetStartTime() const = 0;
+
   // Returns Time represented by presentation timestamp 0.
   // If the timstamps are not associated with a Time, then
   // a null Time is returned.
   virtual base::Time GetTimelineOffset() const = 0;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(Demuxer);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_DEMUXER_H_