Test and fix for huge bwe drop after alr state.

webrtc/modules/congestion_controller/acknowledged_bitrate_estimator.h

+/*
+ *  Copyright (c) 2017 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 WEBRTC_MODULES_CONGESTION_CONTROLLER_ACKNOWLEDGED_BITRATE_ESTIMATOR_H_
+#define WEBRTC_MODULES_CONGESTION_CONTROLLER_ACKNOWLEDGED_BITRATE_ESTIMATOR_H_
+
+#include <memory>
+#include <vector>
+
+#include "webrtc/base/optional.h"
+#include "webrtc/modules/congestion_controller/bitrate_estimator.h"
+
+namespace webrtc {
+
+struct PacketFeedback;
+
+class BitrateEstimatorCreator {
+ public:
+  virtual ~BitrateEstimatorCreator() = default;
+  virtual std::unique_ptr<BitrateEstimator> Create() const;
+};
+
+class AcknowledgedBitrateEstimator {
+ public:
+  AcknowledgedBitrateEstimator(
+      std::unique_ptr<BitrateEstimatorCreator> bitrate_estimator_creator);
+
+  void IncomingPacketFeedbackVector(
+      const std::vector<PacketFeedback>& packet_feedback_vector,
+      bool alr_state);
+  rtc::Optional<uint32_t> bitrate_bps() const;
+
+ private:
+  bool SentInAlrState(const PacketFeedback& packet);
+  bool HasLeftAlrState(bool alr_state) const;
+  bool HasRecentlyLeftAlrState() const;
+  void MaybeResetBitrateEstimator(bool alr_state);
+
+  bool last_alr_state_;
+  rtc::Optional<int64_t> left_alr_state_ms_;
+  const std::unique_ptr<BitrateEstimatorCreator> bitrate_estimator_creator_;
+  std::unique_ptr<BitrateEstimator> bitrate_estimator_;
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_CONGESTION_CONTROLLER_ACKNOWLEDGED_BITRATE_ESTIMATOR_H_