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/avfoundationvideocapturer.mm b/webrtc/sdk/objc/Framework/Classes/avfoundationvideocapturer.mm
index 529499b..51003ca 100644
--- a/webrtc/sdk/objc/Framework/Classes/avfoundationvideocapturer.mm
+++ b/webrtc/sdk/objc/Framework/Classes/avfoundationvideocapturer.mm
@@ -718,7 +718,7 @@
   }
 
   OnFrame(cricket::WebRtcVideoFrame(buffer, webrtc::kVideoRotation_0,
-                                    translated_camera_time_us),
+                                    translated_camera_time_us, 0),
           captured_width, captured_height);
 
   CVBufferRelease(image_buffer);