Unblock and add flag counts for gfe2_reloadable_flag_quic_receive_ack_frequency.

This change removes the enabling_blocked_by field and adds QUIC_RELOADABLE_FLAG_COUNT_N macros to track usage of the ACK_FREQUENCY processing logic.

This code never sends ACK_FREQUENCY or IMMEDIATE_ACK. It advertises the capability to receive it and honors the frames when they arrive.

PiperOrigin-RevId: 874680191

quiche/quic/core/quic_connection.cc

diff --git a/quiche/quic/core/quic_connection.cc b/quiche/quic/core/quic_connection.cc
index d11c8f5..a20c97e 100644
--- a/quiche/quic/core/quic_connection.cc
+++ b/quiche/quic/core/quic_connection.cc
@@ -2196,6 +2196,7 @@
                     ConnectionCloseBehavior::SEND_CONNECTION_CLOSE_PACKET);
     return false;
   }
+  QUIC_RELOADABLE_FLAG_COUNT_N(quic_receive_ack_frequency, 3, 7);
   if (auto packet_number_space =
           QuicUtils::GetPacketNumberSpace(
               last_received_packet_info_.decrypted_level) == APPLICATION_DATA) {
@@ -2224,7 +2225,7 @@
     QUIC_LOG_EVERY_N_SEC(ERROR, 120) << "Got unexpected ImmediateAck Frame.";
     return false;
   }
-  QUIC_RELOADABLE_FLAG_COUNT_N(quic_receive_ack_frequency, 1, 2);
+  QUIC_RELOADABLE_FLAG_COUNT_N(quic_receive_ack_frequency, 1, 7);
   if (last_received_packet_info_.decrypted_level == ENCRYPTION_FORWARD_SECURE) {
     uber_received_packet_manager_.OnImmediateAckFrame();
   } else {

quiche/quic/core/quic_received_packet_manager.cc

diff --git a/quiche/quic/core/quic_received_packet_manager.cc b/quiche/quic/core/quic_received_packet_manager.cc
index 39aba3a..11bd357 100644
--- a/quiche/quic/core/quic_received_packet_manager.cc
+++ b/quiche/quic/core/quic_received_packet_manager.cc
@@ -286,7 +286,7 @@
 
   if (ack_now_) {
     // An IMMEDIATE_ACK frame arrived. Send an ack immediately.
-    QUIC_RELOADABLE_FLAG_COUNT_N(quic_receive_ack_frequency, 2, 2);
+    QUIC_RELOADABLE_FLAG_COUNT_N(quic_receive_ack_frequency, 2, 7);
     ack_timeout_ = now;
     return;
   }
@@ -298,6 +298,9 @@
         last_sent_largest_acked_ >= QuicPacketNumber(reordering_threshold_) &&
         (last_received_packet_number <=
          last_sent_largest_acked_ - reordering_threshold_)) {
+      if (reordering_threshold_ > 1) {
+        QUIC_RELOADABLE_FLAG_COUNT_N(quic_receive_ack_frequency, 7, 7);
+      }
       // Ack immediately if the received packet number is less than or equal to
       // largest acked - reordering threshold.
       ack_timeout_ = now;
@@ -347,10 +350,14 @@
          last_sent_largest_acked_ < ack_frame_.packets.begin()->max() - 1)) {
       // If the lowest ACK range has not yet been reported, and might be trimmed
       // on the next packet arrival, send an ACK.
+      // This is an extreme case; it would be unsurprising if it never happened
+      // in production.
+      QUIC_RELOADABLE_FLAG_COUNT_N(quic_receive_ack_frequency, 6, 7);
       ack_timeout_ = now;
       return;
     }
     if (ReorderingExceedsThreshold()) {
+      QUIC_RELOADABLE_FLAG_COUNT_N(quic_receive_ack_frequency, 5, 7);
       ack_timeout_ = now;
       return;
     }
@@ -395,6 +402,8 @@
                                      // threshold.
     return false;
   }
+  // Cannot get here unless an ACK_FREQUENCY frame was received.
+  QUIC_RELOADABLE_FLAG_COUNT_N(quic_receive_ack_frequency, 4, 7);
   if (!HasMissingPackets() ||
       GetLargestObserved() < QuicPacketNumber(reordering_threshold_)) {
     return false;