Wire up BWE stats through WebrtcSession so that they are filled in both for audio and video calls.

webrtc/pc/webrtcsession.cc

Index: webrtc/pc/webrtcsession.cc
diff --git a/webrtc/pc/webrtcsession.cc b/webrtc/pc/webrtcsession.cc
index cc424b222e081c994b6a7e546f59c126d86a7c01..a7f97885f02c959cee39ce9165fdc228354888d2 100644
--- a/webrtc/pc/webrtcsession.cc
+++ b/webrtc/pc/webrtcsession.cc
@@ -1895,6 +1895,10 @@ bool WebRtcSession::CreateDataChannel(const cricket::ContentInfo* content,
   return true;
 }
 
+Call::Stats WebRtcSession::GetCallStats() {
+  return call_->GetStats();
+}
+
 std::unique_ptr<SessionStats> WebRtcSession::GetStats_n(
     const ChannelNamePairs& channel_name_pairs) {
   RTC_DCHECK(network_thread()->IsCurrent());