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

Passing transport_frame_id() to VideoSink will allow to identify incoming video
frames, which will make it possible to correlate video frames on the
sender and on the receiver.

BUG=chromium:621691
R=mflodman@webrtc.org, stefan@webrtc.org

Review URL: https://codereview.webrtc.org/2088953002 .

Cr-Commit-Position: refs/heads/master@{#13596}
diff --git a/webrtc/sdk/objc/Framework/Classes/RTCVideoRendererAdapter.mm b/webrtc/sdk/objc/Framework/Classes/RTCVideoRendererAdapter.mm
index d810095..a130d0e 100644
--- a/webrtc/sdk/objc/Framework/Classes/RTCVideoRendererAdapter.mm
+++ b/webrtc/sdk/objc/Framework/Classes/RTCVideoRendererAdapter.mm
@@ -36,9 +36,9 @@
       rtc::scoped_refptr<webrtc::VideoFrameBuffer> i420Buffer =
           nativeVideoFrame.video_frame_buffer()->NativeToI420Buffer();
       std::unique_ptr<cricket::VideoFrame> cpuFrame(
-          new cricket::WebRtcVideoFrame(i420Buffer,
-                                        nativeVideoFrame.rotation(),
-                                        nativeVideoFrame.timestamp_us()));
+          new cricket::WebRtcVideoFrame(i420Buffer, nativeVideoFrame.rotation(),
+                                        nativeVideoFrame.timestamp_us(),
+                                        nativeVideoFrame.transport_frame_id()));
       const cricket::VideoFrame *rotatedFrame =
           cpuFrame->GetCopyWithRotationApplied();
       videoFrame = [[RTCVideoFrame alloc] initWithNativeFrame:rotatedFrame];