Add thread-checking to TransportFeedbackAdapter

webrtc/modules/congestion_controller/transport_feedback_adapter.h

 /*
  *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 55 matching lines @@
   rtc::CriticalSection bwe_lock_;
   int transport_overhead_bytes_per_packet_ GUARDED_BY(&lock_);
   SendTimeHistory send_time_history_ GUARDED_BY(&lock_);
   std::unique_ptr<DelayBasedBwe> delay_based_bwe_ GUARDED_BY(&bwe_lock_);
   RtcEventLog* const event_log_;
   Clock* const clock_;
   int64_t current_offset_ms_;
   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
 
 #endif  // WEBRTC_MODULES_CONGESTION_CONTROLLER_TRANSPORT_FEEDBACK_ADAPTER_H_