Implement googContentType GetStats metric reported on receive side.

webrtc/api/statstypes.h

Index: webrtc/api/statstypes.h
diff --git a/webrtc/api/statstypes.h b/webrtc/api/statstypes.h
index 819bfe03af0e466c7dddbc240a8614f15add8672..ec9c9412572476a42a744d8e737557f3f604dc30 100644
--- a/webrtc/api/statstypes.h
+++ b/webrtc/api/statstypes.h
@@ -105,6 +105,7 @@ class StatsReport {
     kStatsValueNameBytesSent,
     kStatsValueNameCodecImplementationName,
     kStatsValueNameConcealedSamples,
+    kStatsValueNameContentType,

[tommi, 2017/08/30 15:03:27]

is this stats value not an 'internal' StatsValue name? (see below)
In general we should avoid adding 'goog' prefixed values and if we do, then I
think (iirc) that those should be considered internal.

[ilnik, 2017/08/30 15:30:24]

Yes, It should be in the internal values below. Moved it and another one I've
added recently there.

     kStatsValueNameDataChannelId,
     kStatsValueNameFramesDecoded,
     kStatsValueNameFramesEncoded,