Fix to ensure hybrid slow start is reset when QUIC's retransmission

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/rtt_stats.h"
@@ skipping 251 matching lines @@
     DVLOG(1) << "Cubic; congestion window: " << congestion_window_
              << " slowstart threshold: " << slowstart_threshold_;
   }
 }
 
 void TcpCubicSender::OnRetransmissionTimeout(bool packets_retransmitted) {
   bytes_in_flight_ = 0;
   largest_sent_at_last_cutback_ = 0;
   if (packets_retransmitted) {
     cubic_.Reset();
+    hybrid_slow_start_.Restart();
     congestion_window_ = kMinimumCongestionWindow;
   }
 }
 
 void TcpCubicSender::UpdateRtt(QuicTime::Delta rtt) {
-  // Hybrid start triggers when cwnd is larger than some threshold.
   if (InSlowStart() &&
       hybrid_slow_start_.ShouldExitSlowStart(rtt_stats_, congestion_window_)) {
      slowstart_threshold_ = congestion_window_;
   }
 }
 
 void TcpCubicSender::PrrOnPacketLost() {
   prr_out_ = 0;
   bytes_in_flight_before_loss_ = bytes_in_flight_;
   // Since all losses are triggered by an incoming ack currently, and acks are
@@ skipping 28 matching lines @@
   // AvailableSendWindow =
   //   CEIL(prr_delivered * ssthresh / BytesInFlightAtLoss) - prr_sent
   if (prr_delivered_ * slowstart_threshold_ * kMaxSegmentSize >
           prr_out_ * bytes_in_flight_before_loss_) {
     return QuicTime::Delta::Zero();
   }
   return QuicTime::Delta::Infinite();
 }
 
 }  // namespace net