RTCMediaStreamTrackStats.framesDropped collected by RTCStatsCollector.

webrtc/api/rtcstatscollector.cc

 /*
  *  Copyright 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 419 matching lines @@
   video_track_stats->remote_source = true;
   video_track_stats->detached = false;
   if (video_receiver_info.frame_width > 0 &&
       video_receiver_info.frame_height > 0) {
     video_track_stats->frame_width = static_cast<uint32_t>(
         video_receiver_info.frame_width);
     video_track_stats->frame_height = static_cast<uint32_t>(
         video_receiver_info.frame_height);
   }
   video_track_stats->frames_received = video_receiver_info.frames_received;
+  RTC_DCHECK_GE(video_receiver_info.frames_received,
+                video_receiver_info.frames_rendered);
+  video_track_stats->frames_dropped = video_receiver_info.frames_received -
+                                      video_receiver_info.frames_rendered;
   return video_track_stats;
 }
 
 void ProduceMediaStreamAndTrackStats(
     int64_t timestamp_us,
     const TrackMediaInfoMap& track_media_info_map,
     rtc::scoped_refptr<StreamCollectionInterface> streams,
     bool is_local,
     RTCStatsReport* report) {
   // TODO(hbos): When "AddTrack" is implemented we should iterate tracks to
@@ skipping 760 matching lines @@
     const std::string& type) {
   return CandidateTypeToRTCIceCandidateType(type);
 }
 
 const char* DataStateToRTCDataChannelStateForTesting(
     DataChannelInterface::DataState state) {
   return DataStateToRTCDataChannelState(state);
 }
 
 }  // namespace webrtc