Add tracing to interesting media-related methods.

webrtc/media/engine/webrtcvideoengine2.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 1200 matching lines @@
       receive_streams_.find(ssrc);
   if (it == receive_streams_.end()) {
     return false;
   }
 
   it->second->SetSink(sink);
   return true;
 }
 
 bool WebRtcVideoChannel2::GetStats(VideoMediaInfo* info) {
+  TRACE_EVENT0("webrtc", "WebRtcVideoChannel2::GetStats");
   info->Clear();
   FillSenderStats(info);
   FillReceiverStats(info);
   webrtc::Call::Stats stats = call_->GetStats();
   FillBandwidthEstimationStats(stats, info);
   if (stats.rtt_ms != -1) {
     for (size_t i = 0; i < info->senders.size(); ++i) {
       info->senders[i].rtt_ms = stats.rtt_ms;
     }
   }
@@ skipping 1283 matching lines @@
         rtx_mapping[video_codecs[i].codec.id] !=
             fec_settings.red_payload_type) {
       video_codecs[i].rtx_payload_type = rtx_mapping[video_codecs[i].codec.id];
     }
   }
 
   return video_codecs;
 }
 
 }  // namespace cricket