Implement framesDecoded stat in video receive ssrc stats.

webrtc/media/base/mediachannel.h

Index: webrtc/media/base/mediachannel.h
diff --git a/webrtc/media/base/mediachannel.h b/webrtc/media/base/mediachannel.h
index 68f7df179c2db20edad713fe97536bea43567de0..2b5134dd7544d0e3973b24d2bf7d5bd05afbc38a 100644
--- a/webrtc/media/base/mediachannel.h
+++ b/webrtc/media/base/mediachannel.h
@@ -700,6 +700,7 @@ struct VideoReceiverInfo : public MediaReceiverInfo {
         framerate_output(0),
         framerate_render_input(0),
         framerate_render_output(0),
+        frames_decoded(0),
         decode_ms(0),
         max_decode_ms(0),
         jitter_buffer_ms(0),
@@ -725,6 +726,7 @@ struct VideoReceiverInfo : public MediaReceiverInfo {
   int framerate_render_input;
   // Framerate that the renderer reports.
   int framerate_render_output;
+  uint32_t frames_decoded;
 
   // All stats below are gathered per-VideoReceiver, but some will be correlated
   // across MediaStreamTracks.  NOTE(hta): when sinking stats into per-SSRC