Update from https://crrev.com/304418

net/quic/congestion_control/tcp_cubic_sender.cc

 // 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.
 
 #include "net/quic/congestion_control/tcp_cubic_sender.h"
 
 #include <algorithm>
 
 #include "base/metrics/histogram.h"
 #include "net/quic/congestion_control/prr_sender.h"
@@ skipping 13 matching lines @@
 const QuicByteCount kMaxSegmentSize = kDefaultTCPMSS;
 const int kMaxBurstLength = 3;
 const float kRenoBeta = 0.7f;  // Reno backoff factor.
 const uint32 kDefaultNumConnections = 2;  // N-connection emulation.
 }  // namespace
 
 TcpCubicSender::TcpCubicSender(
     const QuicClock* clock,
     const RttStats* rtt_stats,
     bool reno,
+    QuicPacketCount initial_tcp_congestion_window,
     QuicPacketCount max_tcp_congestion_window,
     QuicConnectionStats* stats)
     : hybrid_slow_start_(clock),
       cubic_(clock, stats),
       rtt_stats_(rtt_stats),
       stats_(stats),
       reno_(reno),
       num_connections_(kDefaultNumConnections),
       congestion_window_count_(0),
       largest_sent_sequence_number_(0),
       largest_acked_sequence_number_(0),
       largest_sent_at_last_cutback_(0),
-      congestion_window_(kDefaultInitialWindow),
+      congestion_window_(initial_tcp_congestion_window),
       previous_congestion_window_(0),
       slowstart_threshold_(max_tcp_congestion_window),
       previous_slowstart_threshold_(0),
       last_cutback_exited_slowstart_(false),
       max_tcp_congestion_window_(max_tcp_congestion_window) {
 }
 
 TcpCubicSender::~TcpCubicSender() {
   UMA_HISTOGRAM_COUNTS("Net.QuicSession.FinalTcpCwnd", congestion_window_);
 }
 
-void TcpCubicSender::SetFromConfig(const QuicConfig& config, bool is_server) {
+void TcpCubicSender::SetFromConfig(const QuicConfig& config,
+                                   bool is_server,
+                                   bool using_pacing) {
   if (is_server) {
     if (config.HasReceivedConnectionOptions() &&
         ContainsQuicTag(config.ReceivedConnectionOptions(), kIW10)) {
-      // Initial window experiment.  Ignore the initial congestion
-      // window suggested by the client and use the default ICWND of
-      // 10 instead.
-      congestion_window_ = kDefaultInitialWindow;
-    } else if (config.HasReceivedInitialCongestionWindow()) {
-      // Set the initial window size.
-      congestion_window_ = max(kMinimumCongestionWindow,
-          min(kMaxInitialWindow,
-              static_cast<QuicPacketCount>(
-                  config.ReceivedInitialCongestionWindow())));
+      // Initial window experiment.
+      congestion_window_ = 10;
+    }
+    if (using_pacing) {
+      // Disable the ack train mode in hystart when pacing is enabled, since it
+      // may be falsely triggered.
+      hybrid_slow_start_.set_ack_train_detection(false);
     }
   }
 }
 
 void TcpCubicSender::SetNumEmulatedConnections(int num_connections) {
   num_connections_ = max(1, num_connections);
   cubic_.SetNumConnections(num_connections_);
 }
 
 float TcpCubicSender::RenoBeta() const {
@@ skipping 252 matching lines @@
   congestion_window_ = previous_congestion_window_;
   slowstart_threshold_ = previous_slowstart_threshold_;
   previous_congestion_window_ = 0;
 }
 
 CongestionControlType TcpCubicSender::GetCongestionControlType() const {
   return reno_ ? kReno : kCubic;
 }
 
 }  // namespace net