Add receive bitrates to histogram stats:

- total bitrate ("WebRTC.Video.BitrateReceivedInKbps")
- media bitrate ("WebRTC.Video.MediaBitrateReceivedInKbps")
- rtx bitrate ("WebRTC.Video.RtxBitrateReceivedInKbps")
- padding bitrate ("WebRTC.Video.PaddingBitrateReceivedInKbps")

BUG=crbug/419657
R=mflodman@webrtc.org, stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/27189005

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7756 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/modules/rtp_rtcp/interface/rtp_payload_registry.h

@@ -77,6 +77,8 @@ class RTPPayloadRegistry {
 
   void SetRtxSsrc(uint32_t ssrc);
 
+  bool GetRtxSsrc(uint32_t* ssrc) const;
+
   void SetRtxPayloadType(int payload_type);
 
   bool IsRtx(const RTPHeader& header) const;