Preliminary change for new rtc rendering algorithm

media/base/video_frame.h

Index: media/base/video_frame.h
diff --git a/media/base/video_frame.h b/media/base/video_frame.h
index bc92b9a0fcaee3c460ee2cf493b2629cae7c2fc7..e500853f5bd697f9a6b0467172fe48556408e2cf 100644
--- a/media/base/video_frame.h
+++ b/media/base/video_frame.h
@@ -365,6 +365,9 @@ class MEDIA_EXPORT VideoFrame : public base::RefCountedThreadSafe<VideoFrame> {
   const VideoFrameMetadata* metadata() const { return &metadata_; }
   VideoFrameMetadata* metadata() { return &metadata_; }
 
+  // The time span between the current frame and the first frame of the stream.
+  // This is the media timestamp, and not the reference time.
+  // See VideoFrameMetadata::REFERENCE_TIME for details.
   base::TimeDelta timestamp() const { return timestamp_; }
   void set_timestamp(base::TimeDelta timestamp) {
     timestamp_ = timestamp;