gfe-relnote: Add support for 1RTT and 2RTT connection options in BBRv2, which reduce the number of rounds in STARTUP without a 25% bandwidth increase to 1 and 2 round trips, respectively.  Protected by gfe2_reloadable_flag_quic_bbr2_fewer_startup_round_trips.

PiperOrigin-RevId: 306924645
Change-Id: I3fb267f0abe90811772ddc78130aaa7a18c3e705

quic/core/congestion_control/bbr2_sender.cc

diff --git a/quic/core/congestion_control/bbr2_sender.cc b/quic/core/congestion_control/bbr2_sender.cc
index a367a56..8428bb5 100644
--- a/quic/core/congestion_control/bbr2_sender.cc
+++ b/quic/core/congestion_control/bbr2_sender.cc
@@ -119,6 +119,16 @@
       config.HasClientRequestedIndependentOption(kB2CL, perspective)) {
     params_.avoid_too_low_probe_bw_cwnd = false;
   }
+  if (GetQuicReloadableFlag(quic_bbr2_fewer_startup_round_trips) &&
+      config.HasClientRequestedIndependentOption(k1RTT, perspective)) {
+    QUIC_RELOADABLE_FLAG_COUNT_N(quic_bbr2_fewer_startup_round_trips, 1, 2);
+    params_.startup_full_bw_rounds = 1;
+  }
+  if (GetQuicReloadableFlag(quic_bbr2_fewer_startup_round_trips) &&
+      config.HasClientRequestedIndependentOption(k2RTT, perspective)) {
+    QUIC_RELOADABLE_FLAG_COUNT_N(quic_bbr2_fewer_startup_round_trips, 2, 2);
+    params_.startup_full_bw_rounds = 2;
+  }
 }
 
 Limits<QuicByteCount> Bbr2Sender::GetCwndLimitsByMode() const {