Probing: Add support for exponential startup probing

webrtc/modules/congestion_controller/delay_based_bwe.h

 /*
  *  Copyright (c) 2016 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 39 matching lines @@
   // Required by RemoteBitrateEstimator but does nothing.
   void RemoveStream(uint32_t ssrc) override;
   void IncomingPacket(int64_t arrival_time_ms,
                       size_t payload_size,
                       const RTPHeader& header) override {
     RTC_NOTREACHED();
   }
 
  private:
   void IncomingPacketInfo(const PacketInfo& info);
+  // Updates the current remote rate estimate and returns true if a valid
+  // estimate exists.
+  bool UpdateEstimate(int64_t packet_arrival_time_ms,
+                      int64_t now_ms,
+                      uint32_t* target_bitrate_bps)
+      EXCLUSIVE_LOCKS_REQUIRED(crit_);
 
   rtc::ThreadChecker network_thread_;
   Clock* const clock_;
   RemoteBitrateObserver* const observer_;
   std::unique_ptr<InterArrival> inter_arrival_;
   std::unique_ptr<OveruseEstimator> estimator_;
   OveruseDetector detector_;
   RateStatistics incoming_bitrate_;
-  int64_t first_packet_time_ms_;
   int64_t last_update_ms_;
   int64_t last_seen_packet_ms_;
   bool uma_recorded_;
 
   rtc::CriticalSection crit_;
   AimdRateControl remote_rate_ GUARDED_BY(&crit_);
   ProbeBitrateEstimator probe_bitrate_estimator_ GUARDED_BY(&crit_);
 
   RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(DelayBasedBwe);
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_CONGESTION_CONTROLLER_DELAY_BASED_BWE_H_