Introduce DecodeTimestamp class to make it easier to distiguish presentation and decode timestamps.

media/filters/frame_processor.h

Index: media/filters/frame_processor.h
diff --git a/media/filters/frame_processor.h b/media/filters/frame_processor.h
index 0cd24f1b06cc5dbf3cdcaff64114528eed67aa26..0afcf0ae17fc4be7fabd6c391db95bf3ab68256f 100644
--- a/media/filters/frame_processor.h
+++ b/media/filters/frame_processor.h
@@ -98,8 +98,8 @@ class MEDIA_EXPORT FrameProcessor {
   MseTrackBuffer* FindTrack(StreamParser::TrackId id);
 
   // Signals all track buffers' streams that a new media segment is starting
-  // with timestamp |segment_timestamp|.
-  void NotifyNewMediaSegmentStarting(base::TimeDelta segment_timestamp);
+  // with decode timestamp |segment_timestamp|.
+  void NotifyNewMediaSegmentStarting(DecodeTimestamp segment_timestamp);
 
   // Helper that signals each track buffer to append any processed, but not yet
   // appended, frames to its stream. Returns true on success, or false if one or