Reduce usage of tmmbr information structure
by creating it on accepted tmmbr/tmmbn rtcp messages
rather on sender/receiver reports.

BUG=webrtc:5565

Review-Url: https://codereview.webrtc.org/2702373002
Cr-Commit-Position: refs/heads/master@{#16748}
diff --git a/webrtc/modules/rtp_rtcp/source/rtcp_receiver.h b/webrtc/modules/rtp_rtcp/source/rtcp_receiver.h
index c00e7ee..c64e95d 100644
--- a/webrtc/modules/rtp_rtcp/source/rtcp_receiver.h
+++ b/webrtc/modules/rtp_rtcp/source/rtcp_receiver.h
@@ -131,7 +131,10 @@
   void TriggerCallbacksFromRtcpPacket(
       const PacketInformation& packet_information);
 
-  void CreateTmmbrInformation(uint32_t remote_ssrc)
+  TmmbrInformation* FindOrCreateTmmbrInfo(uint32_t remote_ssrc)
+      EXCLUSIVE_LOCKS_REQUIRED(rtcp_receiver_lock_);
+  // Update TmmbrInformation (if present) is alive.
+  void UpdateTmmbrRemoteIsAlive(uint32_t remote_ssrc)
       EXCLUSIVE_LOCKS_REQUIRED(rtcp_receiver_lock_);
   TmmbrInformation* GetTmmbrInformation(uint32_t remote_ssrc)
       EXCLUSIVE_LOCKS_REQUIRED(rtcp_receiver_lock_);