Update from chromium https://crrev.com/302282

net/quic/congestion_control/tcp_loss_algorithm.h

 // Copyright 2014 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.
 
 #ifndef NET_QUIC_CONGESTION_CONTROL_TCP_LOSS_ALGORITHM_H_
 #define NET_QUIC_CONGESTION_CONTROL_TCP_LOSS_ALGORITHM_H_
 
 #include <algorithm>
 #include <map>
 
 #include "base/basictypes.h"
 #include "net/quic/congestion_control/loss_detection_interface.h"
 #include "net/quic/quic_protocol.h"
 #include "net/quic/quic_time.h"
 #include "net/quic/quic_unacked_packet_map.h"
 
 namespace net {
 
 // Class which implement's TCP's approach of detecting loss when 3 nacks have
 // been received for a packet.  Also implements TCP's early retransmit(RFC5827).
 class NET_EXPORT_PRIVATE TCPLossAlgorithm : public LossDetectionInterface {
  public:
+  // TCP retransmits after 3 nacks.
+  static const size_t kNumberOfNacksBeforeRetransmission = 3;
+
   TCPLossAlgorithm();
   ~TCPLossAlgorithm() override {}
 
   LossDetectionType GetLossDetectionType() const override;
 
   // Uses nack counts to decide when packets are lost.
   SequenceNumberSet DetectLostPackets(
       const QuicUnackedPacketMap& unacked_packets,
       const QuicTime& time,
       QuicPacketSequenceNumber largest_observed,
       const RttStats& rtt_stats) override;
 
   // Returns a non-zero value when the early retransmit timer is active.
   QuicTime GetLossTimeout() const override;
 
  private:
   QuicTime loss_detection_timeout_;
 
   DISALLOW_COPY_AND_ASSIGN(TCPLossAlgorithm);
 };
 
 }  // namespace net
 
 #endif  // NET_QUIC_CONGESTION_CONTROL_TCP_LOSS_ALGORITHM_H_