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

webrtc/media/base/videoframefactory.cc

 /*
  *  Copyright (c) 2014 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 26 matching lines @@
       (input_frame->rotation == webrtc::kVideoRotation_90 ||
        input_frame->rotation == webrtc::kVideoRotation_270)) {
     std::swap(output_width, output_height);
   }
 
   rtc::scoped_refptr<webrtc::I420Buffer> scaled_buffer(
       pool_.CreateBuffer(output_width, output_height));
   scaled_buffer->CropAndScaleFrom(cropped_input_frame->video_frame_buffer());
 
   return new WebRtcVideoFrame(scaled_buffer, cropped_input_frame->rotation(),
-                              cropped_input_frame->timestamp_us());
+                              cropped_input_frame->timestamp_us(),
+                              cropped_input_frame->transport_frame_id());
 }
 
 }  // namespace cricket