Deprecate --gfe2_reloadable_flag_quic_bbr2_flip_bbq2.

Startblock:
   after 2020-10-27 10:30 in Google/US-CAM
PiperOrigin-RevId: 339253198
Change-Id: I22d11b5b612a3b40300d0297e8b1530620258a29

quic/core/congestion_control/bbr2_misc.h

diff --git a/quic/core/congestion_control/bbr2_misc.h b/quic/core/congestion_control/bbr2_misc.h
index 0872076..2287960 100644
--- a/quic/core/congestion_control/bbr2_misc.h
+++ b/quic/core/congestion_control/bbr2_misc.h
@@ -76,8 +76,7 @@
    */
 
   // The gain for both CWND and PacingRate at startup.
-  float startup_cwnd_gain =
-      GetQuicReloadableFlag(quic_bbr2_flip_bbq2) ? 2.0 : 2.885;
+  float startup_cwnd_gain = 2.0;
   // TODO(wub): Maybe change to the newly derived value of 2.773 (4 * ln(2)).
   float startup_pacing_gain = 2.885;
 
@@ -99,8 +98,7 @@
   /*
    * DRAIN parameters.
    */
-  float drain_cwnd_gain =
-      GetQuicReloadableFlag(quic_bbr2_flip_bbq2) ? 2.0 : 2.885;
+  float drain_cwnd_gain = 2.0;
   float drain_pacing_gain = 1.0 / 2.885;
 
   /*

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 6761202..a2e23bf 100644
--- a/quic/core/congestion_control/bbr2_sender.cc
+++ b/quic/core/congestion_control/bbr2_sender.cc
@@ -148,14 +148,8 @@
 void Bbr2Sender::ApplyConnectionOptions(
     const QuicTagVector& connection_options) {
   if (ContainsQuicTag(connection_options, kBBQ2)) {
-    if (GetQuicReloadableFlag(quic_bbr2_flip_bbq2)) {
-      params_.startup_cwnd_gain = 2.885;
-      params_.drain_cwnd_gain = 2.885;
-    } else {
-      // 2 is the lower, derived gain for CWND.
-      params_.startup_cwnd_gain = 2;
-      params_.drain_cwnd_gain = 2;
-    }
+    params_.startup_cwnd_gain = 2.885;
+    params_.drain_cwnd_gain = 2.885;
   }
   if (GetQuicReloadableFlag(quic_bbr2_no_exit_startup_on_loss_with_bw_growth) &&
       ContainsQuicTag(connection_options, kB2NE)) {

quic/core/congestion_control/bbr2_simulator_test.cc

diff --git a/quic/core/congestion_control/bbr2_simulator_test.cc b/quic/core/congestion_control/bbr2_simulator_test.cc
index c769bff..022dba8 100644
--- a/quic/core/congestion_control/bbr2_simulator_test.cc
+++ b/quic/core/congestion_control/bbr2_simulator_test.cc
@@ -623,17 +623,9 @@
   EXPECT_APPROX_EQ(sender_->BandwidthEstimate() * (1 / 2.885f),
                    sender_->PacingRate(0), 0.01f);
 
-  if (GetQuicReloadableFlag(quic_bbr2_flip_bbq2)) {
-    // BBR uses CWND gain of 2 during STARTUP, hence it will fill the buffer
-    // with approximately 1 BDP.  Here, we use 0.95 to give some margin for
-    // error.
-    EXPECT_GE(queue->bytes_queued(), 0.95 * params.BDP());
-  } else {
-    // BBR uses CWND gain of 2.88 during STARTUP, hence it will fill the buffer
-    // with approximately 1.88 BDPs.  Here, we use 1.5 to give some margin for
-    // error.
-    EXPECT_GE(queue->bytes_queued(), 1.5 * params.BDP());
-  }
+  // BBR uses CWND gain of 2 during STARTUP, hence it will fill the buffer with
+  // approximately 1 BDP.  Here, we use 0.95 to give some margin for error.
+  EXPECT_GE(queue->bytes_queued(), 0.95 * params.BDP());
 
   // Observe increased RTT due to bufferbloat.
   const QuicTime::Delta queueing_delay =