Implement timestamp translation/filter in VideoCapturer.

webrtc/media/engine/webrtcvideoframefactory.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.
  */
 
 #include <memory>
 
 #include "webrtc/base/logging.h"
 #include "webrtc/media/engine/webrtcvideoframe.h"
 #include "webrtc/media/engine/webrtcvideoframefactory.h"
 
 namespace cricket {
 
 VideoFrame* WebRtcVideoFrameFactory::CreateAliasedFrame(
     const CapturedFrame* aliased_frame, int width, int height) const {
   std::unique_ptr<WebRtcVideoFrame> frame(new WebRtcVideoFrame());
   if (!frame->Init(aliased_frame, width, height, apply_rotation_)) {
     LOG(LS_ERROR) <<
         "Failed to create WebRtcVideoFrame in CreateAliasedFrame.";
     return NULL;
   }
+  frame->set_timestamp_us(frame->timestamp_us() + timestamp_offset_us_);
   return frame.release();
 }
 
 }  // namespace cricket