Deprercate gfe2_reloadable_flag_quic_enable_ack_decimation.

PiperOrigin-RevId: 322387795
Change-Id: Id17e42d2123b76fdae76d1075b5f4a27e7401dbb

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 8ea5217..1ff703d 100644
--- a/quic/core/congestion_control/bbr2_simulator_test.cc
+++ b/quic/core/congestion_control/bbr2_simulator_test.cc
@@ -121,11 +121,7 @@
 
 class Bbr2SimulatorTest : public QuicTest {
  protected:
-  Bbr2SimulatorTest() : simulator_(&random_) {
-    // Disable Ack Decimation by default, because it can significantly increase
-    // srtt. Individual test can enable it via QuicConnectionPeer::SetAckMode().
-    SetQuicReloadableFlag(quic_enable_ack_decimation, false);
-  }
+  Bbr2SimulatorTest() : simulator_(&random_) {}
 
   void SetUp() override {
     if (GetQuicFlag(FLAGS_quic_bbr2_test_regression_mode) == "regress") {
@@ -425,7 +421,7 @@
   DoSimpleTransfer(12 * 1024 * 1024, QuicTime::Delta::FromSeconds(30));
   EXPECT_TRUE(Bbr2ModeIsOneOf({Bbr2Mode::PROBE_BW, Bbr2Mode::PROBE_RTT}));
   EXPECT_APPROX_EQ(params.BottleneckBandwidth(),
-                   sender_->ExportDebugState().bandwidth_hi, 0.01f);
+                   sender_->ExportDebugState().bandwidth_hi, 0.02f);
   EXPECT_GE(sender_connection_stats().packets_lost, 0u);
   EXPECT_FALSE(sender_->ExportDebugState().last_sample_is_app_limited);
 }
@@ -664,7 +660,7 @@
     EXPECT_EQ(Bbr2Mode::PROBE_BW, sender_->ExportDebugState().mode);
     EXPECT_EQ(CyclePhase::PROBE_UP, sender_->ExportDebugState().probe_bw.phase);
     EXPECT_APPROX_EQ(params.BottleneckBandwidth(),
-                     sender_->ExportDebugState().bandwidth_hi, 0.01f);
+                     sender_->ExportDebugState().bandwidth_hi, 0.02f);
   }
 
   // Now that in-flight is almost zero and the pacing gain is still above 1,

quic/core/quic_received_packet_manager.cc

diff --git a/quic/core/quic_received_packet_manager.cc b/quic/core/quic_received_packet_manager.cc
index 017ae2b..942c8b5 100644
--- a/quic/core/quic_received_packet_manager.cc
+++ b/quic/core/quic_received_packet_manager.cc
@@ -41,9 +41,7 @@
       time_largest_observed_(QuicTime::Zero()),
       save_timestamps_(false),
       stats_(stats),
-      ack_mode_(GetQuicReloadableFlag(quic_enable_ack_decimation)
-                    ? ACK_DECIMATION
-                    : TCP_ACKING),
+      ack_mode_(ACK_DECIMATION),
       num_retransmittable_packets_received_since_last_ack_sent_(0),
       min_received_before_ack_decimation_(kMinReceivedBeforeAckDecimation),
       ack_frequency_before_ack_decimation_(
@@ -56,18 +54,13 @@
           QuicTime::Delta::FromMilliseconds(kDefaultDelayedAckTimeMs)),
       ack_timeout_(QuicTime::Zero()),
       time_of_previous_received_packet_(QuicTime::Zero()),
-      was_last_packet_missing_(false) {
-  if (ack_mode_ == ACK_DECIMATION) {
-    QUIC_RELOADABLE_FLAG_COUNT(quic_enable_ack_decimation);
-  }
-}
+      was_last_packet_missing_(false) {}
 
 QuicReceivedPacketManager::~QuicReceivedPacketManager() {}
 
 void QuicReceivedPacketManager::SetFromConfig(const QuicConfig& config,
                                               Perspective perspective) {
-  if (GetQuicReloadableFlag(quic_enable_ack_decimation) &&
-      config.HasClientSentConnectionOption(kACD0, perspective)) {
+  if (config.HasClientSentConnectionOption(kACD0, perspective)) {
     ack_mode_ = TCP_ACKING;
   }
   if (config.HasClientSentConnectionOption(kACKD, perspective)) {