Add WebMediaPlayer::timelineOffset() support to WebMediaPlayerImpl.

media/base/demuxer.h

Index: media/base/demuxer.h
diff --git a/media/base/demuxer.h b/media/base/demuxer.h
index 31c9e29de504e0ad75ee2e19fb1af6f5e0c0f814..581bc0075f6f5023da5970308a6b99614a718861 100644
--- a/media/base/demuxer.h
+++ b/media/base/demuxer.h
@@ -87,6 +87,11 @@ class MEDIA_EXPORT Demuxer {
   // Returns the starting time for the media file.
   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);
 };