Use microsecond timestamp in cricket::VideoFrame.

webrtc/media/base/videobroadcaster.cc

 /*
  *  Copyright (c) 2016 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 81 matching lines @@
     wants.max_pixel_count_step_up = Optional<int>();
   }
   current_wants_ = wants;
 }
 
 const cricket::VideoFrame& VideoBroadcaster::GetBlackFrame(
     const cricket::VideoFrame& frame) {
   if (black_frame_ && black_frame_->width() == frame.width() &&
       black_frame_->height() == frame.height() &&
       black_frame_->rotation() == frame.rotation()) {
-    black_frame_->SetTimeStamp(frame.GetTimeStamp());
+    black_frame_->set_timestamp_us(frame.timestamp_us());
     return *black_frame_;
   }
   black_frame_.reset(new cricket::WebRtcVideoFrame(
-      new rtc::RefCountedObject<webrtc::I420Buffer>(
-          frame.width(), frame.height()),
-      frame.GetTimeStamp(), frame.rotation()));
+      new rtc::RefCountedObject<webrtc::I420Buffer>(frame.width(),
+                                                    frame.height()),
+      frame.rotation(), frame.timestamp_us()));
   black_frame_->SetToBlack();
   return *black_frame_;
 }
 
 }  // namespace rtc