Add time line for acked bitrate.

webrtc/modules/remote_bitrate_estimator/transport_feedback_adapter.cc

Index: webrtc/modules/remote_bitrate_estimator/transport_feedback_adapter.cc
diff --git a/webrtc/modules/remote_bitrate_estimator/transport_feedback_adapter.cc b/webrtc/modules/remote_bitrate_estimator/transport_feedback_adapter.cc
index 217307b86c701c1c85b0f62655097110b80b023b..c0572600d29482987db7ceab8d717e2f0f947f35 100644
--- a/webrtc/modules/remote_bitrate_estimator/transport_feedback_adapter.cc
+++ b/webrtc/modules/remote_bitrate_estimator/transport_feedback_adapter.cc
@@ -70,7 +70,7 @@ void TransportFeedbackAdapter::OnSentPacket(uint16_t sequence_number,
   send_time_history_.OnSentPacket(sequence_number, send_time_ms);
 }
 
-const std::vector<PacketInfo> TransportFeedbackAdapter::GetPacketFeedbackVector(
+std::vector<PacketInfo> TransportFeedbackAdapter::GetPacketFeedbackVector(
     const rtcp::TransportFeedback& feedback) {
   int64_t timestamp_us = feedback.GetBaseTimeUs();
   // Add timestamp deltas to a local time base selected on first packet arrival.
@@ -128,12 +128,13 @@ const std::vector<PacketInfo> TransportFeedbackAdapter::GetPacketFeedbackVector(
   return packet_feedback_vector;
 }
 
-void TransportFeedbackAdapter::OnTransportFeedback(
+std::vector<PacketInfo> TransportFeedbackAdapter::OnTransportFeedback(
     const rtcp::TransportFeedback& feedback) {
   const std::vector<PacketInfo> packet_feedback_vector =
       GetPacketFeedbackVector(feedback);
-  RTC_DCHECK(bitrate_estimator_.get() != nullptr);
-  bitrate_estimator_->IncomingPacketFeedbackVector(packet_feedback_vector);
+  if (bitrate_estimator_.get())
+    bitrate_estimator_->IncomingPacketFeedbackVector(packet_feedback_vector);
+  return packet_feedback_vector;
 }
 
 void TransportFeedbackAdapter::OnReceiveBitrateChanged(