Add thread-checking to TransportFeedbackAdapter

webrtc/modules/congestion_controller/transport_feedback_adapter.h

Index: webrtc/modules/congestion_controller/transport_feedback_adapter.h
diff --git a/webrtc/modules/congestion_controller/transport_feedback_adapter.h b/webrtc/modules/congestion_controller/transport_feedback_adapter.h
index 704970611ce90b26e7b4378d1daf068b18108199..ce85a7bac95fa641ecf80462c86c62ef4f786bff 100644
--- a/webrtc/modules/congestion_controller/transport_feedback_adapter.h
+++ b/webrtc/modules/congestion_controller/transport_feedback_adapter.h
@@ -73,6 +73,20 @@ class TransportFeedbackAdapter : public TransportFeedbackObserver,
   int64_t last_timestamp_us_;
   BitrateController* const bitrate_controller_;
   std::vector<PacketInfo> last_packet_feedback_vector_;
+
+  // Three main threads are in play:
+  //
+  // 1. Data packetized and scheduled for transmission (AddPacket).
+  // 2. After socket sends the data, a notification is produced (OnSentPacket).
+  //    The same thread is also the one on which feedbacks are
+  //    received (OnTransportFeedback).
+  // 3. RTT updates, etc., received from the module process thread (CallStats).
+  //
+  // Note: Not everything falls into this division. GetProbingIntervalMs, for
+  // example, is called from multiple threads.
+  rtc::ThreadChecker packetizer_thread_checker_;
+  rtc::ThreadChecker worker_thread_checker_;
+  rtc::ThreadChecker module_process_thread_checker_;
 };
 
 }  // namespace webrtc