Adds protected bitrate helper methods to RtpRtcpImpl

Bug: webrtc:11036
Change-Id: Iac7f79b60b9f4150868e4e2c59c04c6f866011de
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/158527
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Commit-Queue: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29631}

modules/rtp_rtcp/source/rtp_rtcp_impl.cc

@@ -764,4 +764,12 @@ const RTPSender* ModuleRtpRtcpImpl::RtpSender() const {
   return rtp_sender_.get();
 }
 
+DataRate ModuleRtpRtcpImpl::SendRate() const {
+  return DataRate::bps(rtp_sender_->BitrateSent());
+}
+
+DataRate ModuleRtpRtcpImpl::NackOverheadRate() const {
+  return DataRate::bps(rtp_sender_->NackOverheadRate());
+}
+
 }  // namespace webrtc