RTCMediaStreamTrackStats.kind added and collected.

webrtc/api/rtcstatscollector.cc

Index: webrtc/api/rtcstatscollector.cc
diff --git a/webrtc/api/rtcstatscollector.cc b/webrtc/api/rtcstatscollector.cc
index 5afbb7b32db9347f3e36485156678919cf54c955..7f2f45e84a8a2f7787e37fc3a9c101df0ba288c3 100644
--- a/webrtc/api/rtcstatscollector.cc
+++ b/webrtc/api/rtcstatscollector.cc
@@ -354,7 +354,8 @@ void ProduceMediaStreamAndTrackStats(
         continue;
       }
       std::unique_ptr<RTCMediaStreamTrackStats> audio_track_stats(
-          new RTCMediaStreamTrackStats(id, timestamp_us));
+          new RTCMediaStreamTrackStats(id, timestamp_us,
+                                       RTCMediaStreamTrackKind::kAudio));
       stream_stats->track_ids->push_back(audio_track_stats->id());
       SetMediaStreamTrackStatsFromMediaStreamTrackInterface(
           *audio_track.get(),
@@ -392,7 +393,8 @@ void ProduceMediaStreamAndTrackStats(
         continue;
       }
       std::unique_ptr<RTCMediaStreamTrackStats> video_track_stats(
-          new RTCMediaStreamTrackStats(id, timestamp_us));
+          new RTCMediaStreamTrackStats(id, timestamp_us,
+                                       RTCMediaStreamTrackKind::kVideo));
       stream_stats->track_ids->push_back(video_track_stats->id());
       SetMediaStreamTrackStatsFromMediaStreamTrackInterface(
           *video_track.get(),