webrtc-TransportFeedbackAdapter

TransportFeedbackAdapter
发送端，用于处理接收端来的rtcp-transportCC信息，用于发送端计算基于延迟的估算码率

    TransportFeedbackAdapter(RtcEventLog* event_log,
                       Clock* clock,
                       BitrateController* bitrate_controller)：
                       bitrate_controller_(bitrate_controller) {
             //初始化码率控制器
    }


	//rtcp模块过来的fb包，直接通知bitrate_controller_
	void TransportFeedbackAdapter::OnTransportFeedback(
	    const rtcp::TransportFeedback& feedback) {
	  last_packet_feedback_vector_ = GetPacketFeedbackVector(feedback);
	  DelayBasedBwe::Result result;
	  {
        //估算网络状态等，
	    rtc::CritScope cs(&bwe_lock_);
	    result = delay_based_bwe_->IncomingPacketFeedbackVector(
	        last_packet_feedback_vector_);
	  }

      // 通知码率控制器
	  if (result.updated)
	    bitrate_controller_->OnDelayBasedBweResult(result);
	}