Add cricket::VideoFrame::frame_id() and set it to RTP timestamp.

webrtc/media/base/videoframe.h

Index: webrtc/media/base/videoframe.h
diff --git a/webrtc/media/base/videoframe.h b/webrtc/media/base/videoframe.h
index 4015f906f93c4ee0894d7a7167f4d62bf1b7b7bb..fc9c3d8f4d93c3994fa0c15e1054b5bc7521da58 100644
--- a/webrtc/media/base/videoframe.h
+++ b/webrtc/media/base/videoframe.h
@@ -34,6 +34,9 @@ class VideoFrame {
   virtual const rtc::scoped_refptr<webrtc::VideoFrameBuffer>&
   video_frame_buffer() const = 0;
 
+  // Frame ID. Normally RTP timestamp when the frame was received using RTP.
+  virtual uint32_t frame_id() const = 0;

[stefan-webrtc, 2016/07/28 08:54:49]

Maybe add "transport" to the name to make it more clear that this is something
that only exists after the frame has been sent (or received) over the network
since it's set by the transport layer.

[Sergey Ulanov, 2016/07/29 00:10:22]

Done.

+
   // System monotonic clock, same timebase as rtc::TimeMicros().
   virtual int64_t timestamp_us() const = 0;
   virtual void set_timestamp_us(int64_t time_us) = 0;