Added RTCMediaStreamTrackStats.concealmentEvents

The number of concealment events. This counter increases every time a concealed sample is
synthesized after a non-concealed sample. That is, multiple consecutive concealed samples
will increase the concealedSamples count multiple times but is a single concealment event.

Bug: webrtc:8246
Change-Id: I7ef404edab765218b1f11e3128072c5391e83049
Reviewed-on: https://webrtc-review.googlesource.com/1221
Commit-Queue: Gustaf Ullberg <gustaf@webrtc.org>
Reviewed-by: Henrik Andreassson <henrika@webrtc.org>
Reviewed-by: Fredrik Solenberg <solenberg@webrtc.org>
Reviewed-by: Henrik Lundin <henrik.lundin@webrtc.org>
Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#19881}
diff --git a/api/stats/rtcstats_objects.h b/api/stats/rtcstats_objects.h
index a600fb9..903d266 100644
--- a/api/stats/rtcstats_objects.h
+++ b/api/stats/rtcstats_objects.h
@@ -278,6 +278,7 @@
   RTCStatsMember<uint64_t> total_samples_received;
   RTCStatsMember<double> total_samples_duration;
   RTCStatsMember<uint64_t> concealed_samples;
+  RTCStatsMember<uint64_t> concealment_events;
 };
 
 // https://w3c.github.io/webrtc-stats/#pcstats-dict*