Update from https://crrev.com/304418

net/quic/congestion_control/hybrid_slow_start.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // This class is a helper class to TcpCubicSender.
 // Slow start is the initial startup phase of TCP, it lasts until first packet
 // loss. This class implements hybrid slow start of the TCP cubic send side
 // congestion algorithm. The key feaure of hybrid slow start is that it tries to
 // avoid running into the wall too hard during the slow start phase, which
 // the traditional TCP implementation does.
@@ skipping 35 matching lines @@
   // TODO(ianswett): The following methods should be private, but that requires
   // a follow up CL to update the unit test.
   // Returns true if this ack the last sequence number of our current slow start
   // round.
   // Call Reset if this returns true.
   bool IsEndOfRound(QuicPacketSequenceNumber ack) const;
 
   // Call for the start of each receive round (burst) in the slow start phase.
   void StartReceiveRound(QuicPacketSequenceNumber last_sent);
 
+  void set_ack_train_detection(bool ack_train_detection) {
+    ack_train_detection_ = ack_train_detection;
+  }
+
+  bool ack_train_detection() const {
+    return ack_train_detection_;
+  }
+
   // Whether slow start has started.
   bool started() const {
     return started_;
   }
 
  private:
   // Whether a condition for exiting slow start has been found.
   enum HystartState {
     NOT_FOUND,
     ACK_TRAIN,  // A closely spaced ack train is too long.
     DELAY,  // Too much increase in the round's min_rtt was observed.
   };
 
   const QuicClock* clock_;
+  bool ack_train_detection_;
   // Whether the hybrid slow start has been started.
   bool started_;
   HystartState hystart_found_;
   // Last sequence number sent which was CWND limited.
   QuicPacketSequenceNumber last_sent_sequence_number_;
 
   // Variables for tracking acks received during a slow start round.
   QuicTime round_start_;  // Beginning of each slow start receive round.
   QuicPacketSequenceNumber end_sequence_number_;  // End of the receive round.
   // Last time when the spacing between ack arrivals was less than 2 ms.
   // Defaults to the beginning of the round.
   QuicTime last_close_ack_pair_time_;
   uint32 rtt_sample_count_;  // Number of rtt samples in the current round.
   QuicTime::Delta current_min_rtt_;  // The minimum rtt of current round.
 
   DISALLOW_COPY_AND_ASSIGN(HybridSlowStart);
 };
 
 }  // namespace net
 
 #endif  // NET_QUIC_CONGESTION_CONTROL_HYBRID_SLOW_START_H_