Have AudioSendStream register CNG payload types with the RtpRtcpModule.

webrtc/audio/audio_send_stream.h

Index: webrtc/audio/audio_send_stream.h
diff --git a/webrtc/audio/audio_send_stream.h b/webrtc/audio/audio_send_stream.h
index 56e099fb15a05d6cfc816be6f521890ef5b5878f..dcc28c9dbcb5c807912fe0ec3892bbfbdff57207 100644
--- a/webrtc/audio/audio_send_stream.h
+++ b/webrtc/audio/audio_send_stream.h
@@ -93,6 +93,8 @@ class AudioSendStream final : public webrtc::AudioSendStream,
   void ConfigureBitrateObserver(int min_bitrate_bps, int max_bitrate_bps);
   void RemoveBitrateObserver();
 
+  void RegisterCngPayloadType(int payload_type, int clockrate_hz);
+
   rtc::ThreadChecker worker_thread_checker_;
   rtc::ThreadChecker pacer_thread_checker_;
   rtc::TaskQueue* worker_queue_;