Add average rtt to CallStatsObserver and an average rtt histogram.

webrtc/video_engine/vie_channel_group.cc

Index: webrtc/video_engine/vie_channel_group.cc
diff --git a/webrtc/video_engine/vie_channel_group.cc b/webrtc/video_engine/vie_channel_group.cc
index 4a088c836abb98822d68c1c9062a49d975eb2219..c7de5e1223f9fad76b750dad0f41342b0496b32e 100644
--- a/webrtc/video_engine/vie_channel_group.cc
+++ b/webrtc/video_engine/vie_channel_group.cc
@@ -71,9 +71,9 @@ class WrappingBitrateEstimator : public RemoteBitrateEstimator {
     return rbe_->TimeUntilNextProcess();
   }
 
-  void OnRttUpdate(int64_t rtt) override {
+  void OnRttUpdate(int64_t avg_rtt_ms, int64_t max_rtt_ms) override {
     CriticalSectionScoped cs(crit_sect_.get());
-    rbe_->OnRttUpdate(rtt);
+    rbe_->OnRttUpdate(avg_rtt_ms, max_rtt_ms);
   }
 
   void RemoveStream(unsigned int ssrc) override {