Add support for the MIN1 connection option to TcpCubicBytesSender.

net/quic/congestion_control/tcp_cubic_bytes_sender.cc

Index: net/quic/congestion_control/tcp_cubic_bytes_sender.cc
diff --git a/net/quic/congestion_control/tcp_cubic_bytes_sender.cc b/net/quic/congestion_control/tcp_cubic_bytes_sender.cc
index a5b2f68a25d4e5fed4b7037e37d37168bb509f79..b2489c89c6e0dc5c3f0cbbb661b38e5e04f37991 100644
--- a/net/quic/congestion_control/tcp_cubic_bytes_sender.cc
+++ b/net/quic/congestion_control/tcp_cubic_bytes_sender.cc
@@ -19,7 +19,7 @@ namespace {
 // Constants based on TCP defaults.
 // The minimum cwnd based on RFC 3782 (TCP NewReno) for cwnd reductions on a
 // fast retransmission.
-const QuicByteCount kMinimumCongestionWindow = 2 * kDefaultTCPMSS;
+const QuicByteCount kDefaultMinimumCongestionWindow = 2 * kDefaultTCPMSS;
 const QuicByteCount kMaxSegmentSize = kDefaultTCPMSS;
 const int kMaxBurstLength = 3;
 const float kRenoBeta = 0.7f;             // Reno backoff factor.
@@ -43,6 +43,7 @@ TcpCubicBytesSender::TcpCubicBytesSender(
       largest_acked_sequence_number_(0),
       largest_sent_at_last_cutback_(0),
       congestion_window_(initial_tcp_congestion_window * kMaxSegmentSize),
+      min_congestion_window_(kDefaultMinimumCongestionWindow),
       slowstart_threshold_(std::numeric_limits<uint64>::max()),
       last_cutback_exited_slowstart_(false),
       clock_(clock) {
@@ -60,6 +61,11 @@ void TcpCubicBytesSender::SetFromConfig(const QuicConfig& config,
       // Initial window experiment.
       congestion_window_ = 10 * kMaxSegmentSize;
     }
+    if (config.HasReceivedConnectionOptions() &&
+        ContainsQuicTag(config.ReceivedConnectionOptions(), kMIN1)) {
+      // Min CWND experiment.
+      min_congestion_window_ = kMaxSegmentSize;
+    }
     if (using_pacing) {
       // Disable the ack train mode in hystart when pacing is enabled, since it
       // may be falsely triggered.
@@ -173,8 +179,8 @@ void TcpCubicBytesSender::OnPacketLost(QuicPacketSequenceNumber sequence_number,
   }
   slowstart_threshold_ = congestion_window_;
   // Enforce TCP's minimum congestion window of 2*MSS.
-  if (congestion_window_ < kMinimumCongestionWindow) {
-    congestion_window_ = kMinimumCongestionWindow;
+  if (congestion_window_ < min_congestion_window_) {
+    congestion_window_ = min_congestion_window_;
   }
   largest_sent_at_last_cutback_ = largest_sent_sequence_number_;
   // Reset packet count from congestion avoidance mode. We start counting again
@@ -336,7 +342,7 @@ void TcpCubicBytesSender::OnRetransmissionTimeout(bool packets_retransmitted) {
   cubic_.Reset();
   hybrid_slow_start_.Restart();
   slowstart_threshold_ = congestion_window_ / 2;
-  congestion_window_ = kMinimumCongestionWindow;
+  congestion_window_ = min_congestion_window_;
 }
 
 CongestionControlType TcpCubicBytesSender::GetCongestionControlType() const {