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diff --git a/third_party/libwebrtc/modules/remote_bitrate_estimator/remote_estimator_proxy.h b/third_party/libwebrtc/modules/remote_bitrate_estimator/remote_estimator_proxy.h
new file mode 100644
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+++ b/third_party/libwebrtc/modules/remote_bitrate_estimator/remote_estimator_proxy.h
@@ -0,0 +1,113 @@
+/*
+ *  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.
+ */
+
+#ifndef MODULES_REMOTE_BITRATE_ESTIMATOR_REMOTE_ESTIMATOR_PROXY_H_
+#define MODULES_REMOTE_BITRATE_ESTIMATOR_REMOTE_ESTIMATOR_PROXY_H_
+
+#include <deque>
+#include <functional>
+#include <memory>
+#include <vector>
+
+#include "absl/types/optional.h"
+#include "api/field_trials_view.h"
+#include "api/rtp_headers.h"
+#include "api/transport/network_control.h"
+#include "api/units/data_size.h"
+#include "api/units/time_delta.h"
+#include "api/units/timestamp.h"
+#include "modules/remote_bitrate_estimator/packet_arrival_map.h"
+#include "modules/rtp_rtcp/source/rtcp_packet.h"
+#include "modules/rtp_rtcp/source/rtcp_packet/transport_feedback.h"
+#include "modules/rtp_rtcp/source/rtp_packet_received.h"
+#include "rtc_base/numerics/sequence_number_unwrapper.h"
+#include "rtc_base/synchronization/mutex.h"
+
+namespace webrtc {
+
+// Class used when send-side BWE is enabled: This proxy is instantiated on the
+// receive side. It buffers a number of receive timestamps and then sends
+// transport feedback messages back too the send side.
+class RemoteEstimatorProxy {
+ public:
+  // Used for sending transport feedback messages when send side
+  // BWE is used.
+  using TransportFeedbackSender = std::function<void(
+      std::vector<std::unique_ptr<rtcp::RtcpPacket>> packets)>;
+  RemoteEstimatorProxy(TransportFeedbackSender feedback_sender,
+                       NetworkStateEstimator* network_state_estimator);
+  ~RemoteEstimatorProxy();
+
+  void IncomingPacket(const RtpPacketReceived& packet);
+
+  // Sends periodic feedback if it is time to send it.
+  // Returns time until next call to Process should be made.
+  TimeDelta Process(Timestamp now);
+
+  void OnBitrateChanged(int bitrate);
+  void SetTransportOverhead(DataSize overhead_per_packet);
+
+ private:
+  void MaybeCullOldPackets(int64_t sequence_number, Timestamp arrival_time)
+      RTC_EXCLUSIVE_LOCKS_REQUIRED(&lock_);
+  void SendPeriodicFeedbacks() RTC_EXCLUSIVE_LOCKS_REQUIRED(&lock_);
+  void SendFeedbackOnRequest(int64_t sequence_number,
+                             const FeedbackRequest& feedback_request)
+      RTC_EXCLUSIVE_LOCKS_REQUIRED(&lock_);
+
+  // Returns a Transport Feedback packet with information about as many packets
+  // that has been received between [`begin_sequence_number_incl`,
+  // `end_sequence_number_excl`) that can fit in it. If `is_periodic_update`,
+  // this represents sending a periodic feedback message, which will make it
+  // update the `periodic_window_start_seq_` variable with the first packet that
+  // was not included in the feedback packet, so that the next update can
+  // continue from that sequence number.
+  //
+  // If no incoming packets were added, nullptr is returned.
+  //
+  // `include_timestamps` decide if the returned TransportFeedback should
+  // include timestamps.
+  std::unique_ptr<rtcp::TransportFeedback> MaybeBuildFeedbackPacket(
+      bool include_timestamps,
+      int64_t begin_sequence_number_inclusive,
+      int64_t end_sequence_number_exclusive,
+      bool is_periodic_update) RTC_EXCLUSIVE_LOCKS_REQUIRED(&lock_);
+
+  const TransportFeedbackSender feedback_sender_;
+  Timestamp last_process_time_;
+
+  Mutex lock_;
+  //  `network_state_estimator_` may be null.
+  NetworkStateEstimator* const network_state_estimator_
+      RTC_PT_GUARDED_BY(&lock_);
+  uint32_t media_ssrc_ RTC_GUARDED_BY(&lock_);
+  uint8_t feedback_packet_count_ RTC_GUARDED_BY(&lock_);
+  SeqNumUnwrapper<uint16_t> unwrapper_ RTC_GUARDED_BY(&lock_);
+  DataSize packet_overhead_ RTC_GUARDED_BY(&lock_);
+
+  // The next sequence number that should be the start sequence number during
+  // periodic reporting. Will be absl::nullopt before the first seen packet.
+  absl::optional<int64_t> periodic_window_start_seq_ RTC_GUARDED_BY(&lock_);
+
+  // Packet arrival times, by sequence number.
+  PacketArrivalTimeMap packet_arrival_times_ RTC_GUARDED_BY(&lock_);
+
+  TimeDelta send_interval_ RTC_GUARDED_BY(&lock_);
+  bool send_periodic_feedback_ RTC_GUARDED_BY(&lock_);
+
+  // Unwraps absolute send times.
+  uint32_t previous_abs_send_time_ RTC_GUARDED_BY(&lock_);
+  Timestamp abs_send_timestamp_ RTC_GUARDED_BY(&lock_);
+  Timestamp last_arrival_time_with_abs_send_time_ RTC_GUARDED_BY(&lock_);
+};
+
+}  // namespace webrtc
+
+#endif  //  MODULES_REMOTE_BITRATE_ESTIMATOR_REMOTE_ESTIMATOR_PROXY_H_