Add a new connection option(BBRR) to enable BBR's rate based recovery. Protected by FLAGS_quic_rel…

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 fb02690df2c09e47daeb4051b413be3b429cfa45..3f3714ef14c8ace3d0a3af5d543f2d4f6a202c51 100644
--- a/net/quic/core/congestion_control/bbr_sender.cc
+++ b/net/quic/core/congestion_control/bbr_sender.cc
@@ -119,7 +119,8 @@ BbrSender::BbrSender(const RttStats* rtt_stats,
       recovery_state_(NOT_IN_RECOVERY),
       end_recovery_at_(0),
       recovery_window_(max_congestion_window_),
-      bytes_recently_acked_(0) {
+      bytes_recently_acked_(0),
+      rate_based_recovery_(false) {
   EnterStartupMode();
 }
 
@@ -204,7 +205,7 @@ QuicByteCount BbrSender::GetCongestionWindow() const {
     return kMinimumCongestionWindow;
   }
 
-  if (InRecovery()) {
+  if (InRecovery() && !rate_based_recovery_) {
     return std::min(congestion_window_, recovery_window_);
   }
 
@@ -227,6 +228,10 @@ void BbrSender::SetFromConfig(const QuicConfig& config,
   if (config.HasClientRequestedIndependentOption(k2RTT, perspective)) {
     num_startup_rtts_ = 2;
   }
+  if (FLAGS_quic_reloadable_flag_quic_bbr_rate_recovery &&
+      config.HasClientRequestedIndependentOption(kBBRR, perspective)) {
+    rate_based_recovery_ = true;
+  }
 }
 
 void BbrSender::ResumeConnectionState(
@@ -610,6 +615,10 @@ void BbrSender::CalculatePacingRate() {
   }
 
   QuicBandwidth target_rate = pacing_gain_ * BandwidthEstimate();
+  if (rate_based_recovery_ && InRecovery()) {
+    QUIC_FLAG_COUNT(quic_reloadable_flag_quic_bbr_rate_recovery);
+    pacing_rate_ = pacing_gain_ * max_bandwidth_.GetThirdBest();
+  }
   if (is_at_full_bandwidth_) {
     pacing_rate_ = target_rate;
     return;
@@ -680,6 +689,9 @@ void BbrSender::CalculateCongestionWindow(QuicByteCount bytes_acked) {
 
 void BbrSender::CalculateRecoveryWindow(QuicByteCount bytes_acked,
                                         QuicByteCount bytes_lost) {
+  if (rate_based_recovery_) {
+    return;
+  }
   if (FLAGS_quic_reloadable_flag_quic_bbr_fix_conservation2) {
     if (recovery_state_ == NOT_IN_RECOVERY) {
       return;