Add average rtt to CallStatsObserver and an average rtt histogram.

webrtc/video_engine/vie_channel.h

Index: webrtc/video_engine/vie_channel.h
diff --git a/webrtc/video_engine/vie_channel.h b/webrtc/video_engine/vie_channel.h
index f18ada5d444e4ef2518eb7542853711ae37f16cd..81f4de644573a4d169657f61c3c48a5ca3732ad6 100644
--- a/webrtc/video_engine/vie_channel.h
+++ b/webrtc/video_engine/vie_channel.h
@@ -316,7 +316,7 @@ class ViEChannel : public VCMFrameTypeCallback,
   static bool ChannelDecodeThreadFunction(void* obj);
   bool ChannelDecodeProcess();
 
-  void OnRttUpdate(int64_t rtt);
+  void OnRttUpdate(int64_t avg_rtt_ms, int64_t max_rtt_ms);
 
   int ProtectionRequest(const FecProtectionParams* delta_fec_params,
                         const FecProtectionParams* key_fec_params,
@@ -483,6 +483,10 @@ class ViEChannel : public VCMFrameTypeCallback,
 
   const rtc::scoped_ptr<ReportBlockStats> report_block_stats_sender_;
 
+  int64_t time_of_first_rtt_ms_ GUARDED_BY(crit_);
+  int64_t rtt_sum_ms_ GUARDED_BY(crit_);
+  size_t num_rtts_ GUARDED_BY(crit_);
+
   // RtpRtcp modules, declared last as they use other members on construction.
   const std::vector<RtpRtcp*> rtp_rtcp_modules_;
   size_t num_active_rtp_rtcp_modules_ GUARDED_BY(crit_);