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

webrtc/media/engine/webrtcvideoengine2.cc

Index: webrtc/media/engine/webrtcvideoengine2.cc
diff --git a/webrtc/media/engine/webrtcvideoengine2.cc b/webrtc/media/engine/webrtcvideoengine2.cc
index 3857db9587b9339d82b08b44ffae67e1a91674bf..9af0d875ab140fd62bfdca36df7a57c5c6202fd3 100644
--- a/webrtc/media/engine/webrtcvideoengine2.cc
+++ b/webrtc/media/engine/webrtcvideoengine2.cc
@@ -2432,9 +2432,9 @@ void WebRtcVideoChannel2::WebRtcVideoReceiveStream::OnFrame(
   last_width_ = frame.width();
   last_height_ = frame.height();
 
-  const WebRtcVideoFrame render_frame(

[nisse-webrtc, 2016/06/22 07:46:36]

Why drop const?

[Sergey Ulanov, 2016/06/22 21:22:30]

I just don't think it's useful there, but please let me know if there is a
reason it needs to be there.

+  WebRtcVideoFrame render_frame(
       frame.video_frame_buffer(), frame.rotation(),
-      frame.render_time_ms() * rtc::kNumNanosecsPerMicrosec);
+      frame.render_time_ms() * rtc::kNumNanosecsPerMicrosec, frame.timestamp());
   sink_->OnFrame(render_frame);
 }