Replace interfaces for sending RTCP with std::functions in ReceiveSideCongestionController

Logic for throttling how often REMB messages are sent is added to ReceiveSideCongestionController as well as a new method SetMaxDesiredReceiveBitrate. These are based on the logic in PacketRouter. The logic for throttling REMB and setting the max REMB will be removed from PacketRouter in a follow up cl.
The purpose is to eventually decouple PacketRouter from sending RTCP messages when RtcpTransceiver is used.

Bug: webrtc:12693
Change-Id: I9fb5cbcd14bb17d977e76d329a906fc0a9abc276
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/215685
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Reviewed-by: Christoffer Rodbro <crodbro@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Per Kjellander <perkj@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33801}

modules/congestion_controller/remb_throttler.h

@@ -0,0 +1,54 @@
+/*
+ *  Copyright (c) 2021 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_CONGESTION_CONTROLLER_REMB_THROTTLER_H_
+#define MODULES_CONGESTION_CONTROLLER_REMB_THROTTLER_H_
+
+#include <functional>
+#include <vector>
+
+#include "api/units/data_rate.h"
+#include "api/units/time_delta.h"
+#include "api/units/timestamp.h"
+#include "modules/remote_bitrate_estimator/remote_estimator_proxy.h"
+#include "rtc_base/synchronization/mutex.h"
+
+namespace webrtc {
+
+// RembThrottler is a helper class used for throttling RTCP REMB messages.
+// Throttles small changes to the received BWE within 200ms.
+class RembThrottler : public RemoteBitrateObserver {
+ public:
+  using RembSender =
+      std::function<void(int64_t bitrate_bps, std::vector<uint32_t> ssrcs)>;
+  RembThrottler(RembSender remb_sender, Clock* clock);
+
+  // Ensures the remote party is notified of the receive bitrate no larger than
+  // |bitrate| using RTCP REMB.
+  void SetMaxDesiredReceiveBitrate(DataRate bitrate);
+
+  // Implements RemoteBitrateObserver;
+  // Called every time there is a new bitrate estimate for a receive channel
+  // group. This call will trigger a new RTCP REMB packet if the bitrate
+  // estimate has decreased or if no RTCP REMB packet has been sent for
+  // a certain time interval.
+  void OnReceiveBitrateChanged(const std::vector<uint32_t>& ssrcs,
+                               uint32_t bitrate_bps) override;
+
+ private:
+  const RembSender remb_sender_;
+  Clock* const clock_;
+  mutable Mutex mutex_;
+  Timestamp last_remb_time_ RTC_GUARDED_BY(mutex_);
+  DataRate last_send_remb_bitrate_ RTC_GUARDED_BY(mutex_);
+  DataRate max_remb_bitrate_ RTC_GUARDED_BY(mutex_);
+};
+
+}  // namespace webrtc
+#endif  // MODULES_CONGESTION_CONTROLLER_REMB_THROTTLER_H_