Allow to turn RtcpTransciever on and off at runtime.

Bug: webrtc:8239
Change-Id: I8678d1ee9cd0da194a1243d40b508bb62cb3f257
Reviewed-on: https://webrtc-review.googlesource.com/60180
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22311}

modules/rtp_rtcp/source/rtcp_transceiver.h

@@ -43,6 +43,11 @@ class RtcpTransceiver : public RtcpFeedbackSenderInterface {
       MediaReceiverRtcpObserver* observer,
       std::unique_ptr<rtc::QueuedTask> on_removed);
 
+  // Enables/disables sending rtcp packets eventually.
+  // Packets may be sent after the SetReadyToSend(false) returns, but no new
+  // packets will be scheduled.
+  void SetReadyToSend(bool ready);
+
   // Handles incoming rtcp packets.
   void ReceivePacket(rtc::CopyOnWriteBuffer packet);