Allow QUIC's BBR TCP sender to pace based on min rtt and add an explicit

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 186 matching lines @@
     return QuicTime::Delta::Zero();
   }
   return QuicTime::Delta::Infinite();
 }
 
 QuicByteCount TcpCubicSender::SendWindow() const {
   // What's the current send window in bytes.
   return min(receive_window_, GetCongestionWindow());
 }
 
+QuicBandwidth TcpCubicSender::PacingRate() const {
+  // We pace at twice the rate of the underlying sender's bandwidth estimate
+  // during slow start and 1.25x during congestion avoidance to ensure pacing
+  // doesn't prevent us from filling the window.
+  return BandwidthEstimate().Scale(InSlowStart() ? 2 : 1.25);
+}
+
 QuicBandwidth TcpCubicSender::BandwidthEstimate() const {
   return QuicBandwidth::FromBytesAndTimeDelta(GetCongestionWindow(),
                                               rtt_stats_->SmoothedRtt());
 }
 
 bool TcpCubicSender::HasReliableBandwidthEstimate() const {
   return !InSlowStart() && !InRecovery();
 }
 
 QuicTime::Delta TcpCubicSender::RetransmissionDelay() const {
   if (!rtt_stats_->HasUpdates()) {
     return QuicTime::Delta::Zero();
   }
-  return QuicTime::Delta::FromMicroseconds(
-      rtt_stats_->SmoothedRtt().ToMicroseconds() +
-      4 * rtt_stats_->mean_deviation().ToMicroseconds());
+  return rtt_stats_->SmoothedRtt().Add(
+      rtt_stats_->mean_deviation().Multiply(4));
 }
 
 QuicByteCount TcpCubicSender::GetCongestionWindow() const {
   return congestion_window_ * kMaxSegmentSize;
 }
 
 bool TcpCubicSender::InSlowStart() const {
   return congestion_window_ < slowstart_threshold_;
 }
 
@@ skipping 128 matching lines @@
     return QuicTime::Delta::Zero();
   }
   return QuicTime::Delta::Infinite();
 }
 
 CongestionControlType TcpCubicSender::GetCongestionControlType() const {
   return reno_ ? kReno : kCubic;
 }
 
 }  // namespace net