RTCMediaStreamTrackStats.kind added and collected.

webrtc/api/rtcstats_integrationtest.cc

Index: webrtc/api/rtcstats_integrationtest.cc
diff --git a/webrtc/api/rtcstats_integrationtest.cc b/webrtc/api/rtcstats_integrationtest.cc
index b9e8ac276f33a47d2bfb7d747dd8561b6c820d1f..93f1c6255b95746cba5d1a3293cedad99099e02e 100644
--- a/webrtc/api/rtcstats_integrationtest.cc
+++ b/webrtc/api/rtcstats_integrationtest.cc
@@ -429,9 +429,10 @@ class RTCStatsReportVerifier {
     verifier.TestMemberIsDefined(media_stream_track.remote_source);
     verifier.TestMemberIsDefined(media_stream_track.ended);
     verifier.TestMemberIsDefined(media_stream_track.detached);
+    verifier.TestMemberIsDefined(media_stream_track.kind);
     verifier.TestMemberIsUndefined(media_stream_track.ssrc_ids);
     // Video or audio media stream track?
-    if (media_stream_track.frame_width.is_defined()) {
+    if (*media_stream_track.kind == RTCMediaStreamTrackKind::kVideo) {
       // Video-only members
       verifier.TestMemberIsNonNegative<uint32_t>(
           media_stream_track.frame_width);