getStats: add kind alias for mediaType

see https://github.com/w3c/webrtc-stats/issues/301

IDL: https://w3c.github.io/webrtc-stats/#dom-rtcrtpstreamstats
Change-Id: I7da443bd1cbf07c9a3118ac04329db28b3543b3f

BUG=webrtc:9674

Change-Id: I7da443bd1cbf07c9a3118ac04329db28b3543b3f
Reviewed-on: https://webrtc-review.googlesource.com/96420
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24532}
diff --git a/api/stats/rtcstats_objects.h b/api/stats/rtcstats_objects.h
index 7e6bcd3..a597d6f 100644
--- a/api/stats/rtcstats_objects.h
+++ b/api/stats/rtcstats_objects.h
@@ -337,7 +337,8 @@
   // TODO(hbos): Remote case not supported by |RTCStatsCollector|.
   // crbug.com/657855, 657856
   RTCStatsMember<bool> is_remote;  // = false
-  RTCStatsMember<std::string> media_type;
+  RTCStatsMember<std::string> media_type;  // renamed to kind.
+  RTCStatsMember<std::string> kind;
   RTCStatsMember<std::string> track_id;
   RTCStatsMember<std::string> transport_id;
   RTCStatsMember<std::string> codec_id;