Base QUIC BBR's CWND on SRTT instead of min_rtt. Protected by FLAGS_quic_reloadable_flag_quic_base…

net/quic/core/congestion_control/bbr_sender.cc

Index: net/quic/core/congestion_control/bbr_sender.cc
diff --git a/net/quic/core/congestion_control/bbr_sender.cc b/net/quic/core/congestion_control/bbr_sender.cc
index d02ab68e1e2b4388d7506fa41465deab59ce56ad..c6e89c9df9f87ad91c1fea1767c2e11f420c9f28 100644
--- a/net/quic/core/congestion_control/bbr_sender.cc
+++ b/net/quic/core/congestion_control/bbr_sender.cc
@@ -154,7 +154,11 @@ QuicBandwidth BbrSender::PacingRate(QuicByteCount bytes_in_flight) const {
       mode_ == PROBE_BW && bytes_in_flight > congestion_window_) {
     QUIC_FLAG_COUNT_N(quic_reloadable_flag_quic_bbr_keep_sending_at_recent_rate,
                       1, 2);
-    return max_bandwidth_.GetThirdBest();
+    if (pacing_gain_ > 1) {
+      return max_bandwidth_.GetBest();
+    } else {
+      return max_bandwidth_.GetThirdBest();
+    }
   }
   return pacing_rate_;
 }
@@ -173,7 +177,7 @@ QuicByteCount BbrSender::GetCongestionWindow() const {
   }
 
   if (FLAGS_quic_reloadable_flag_quic_bbr_keep_sending_at_recent_rate &&
-      mode_ == PROBE_BW) {
+      mode_ == PROBE_BW && pacing_gain_ >= 1) {
     QUIC_FLAG_COUNT_N(quic_reloadable_flag_quic_bbr_keep_sending_at_recent_rate,
                       2, 2);
     // Send for another SRTT at a more recently measured bandwidth.
@@ -294,6 +298,10 @@ QuicTime::Delta BbrSender::GetMinRtt() const {
 
 QuicByteCount BbrSender::GetTargetCongestionWindow(float gain) const {
   QuicByteCount bdp = GetMinRtt() * BandwidthEstimate();
+  if (FLAGS_quic_reloadable_flag_quic_bbr_base_cwnd_on_srtt &&
+      mode_ == PROBE_BW && gain >= 1 && !rtt_stats_->smoothed_rtt().IsZero()) {
+    bdp = rtt_stats_->smoothed_rtt() * BandwidthEstimate();
+  }
   QuicByteCount congestion_window = gain * bdp;
 
   // BDP estimate will be zero if no bandwidth samples are available yet.