Implement googContentType GetStats metric reported on receive side.

webrtc/api/statstypes.h

 /*
  *  Copyright 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 87 matching lines @@
 
   enum StatsValueName {
     kStatsValueNameActiveConnection,
     kStatsValueNameAecDivergentFilterFraction,
     kStatsValueNameAudioInputLevel,
     kStatsValueNameAudioOutputLevel,
     kStatsValueNameBytesReceived,
     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,
     kStatsValueNameInterframeDelayMaxMs,  // Max over last 10 seconds.
     kStatsValueNameMediaType,
     kStatsValueNamePacketsLost,
     kStatsValueNamePacketsReceived,
     kStatsValueNamePacketsSent,
     kStatsValueNameProtocol,
     kStatsValueNameQpSum,
@@ skipping 308 matching lines @@
   StatsReport* Find(const StatsReport::Id& id);
 
  private:
   Container list_;
   rtc::ThreadChecker thread_checker_;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_API_STATSTYPES_H_