Deprecate --quic_packet_flusher_check_connected_after_flush_packets.

PiperOrigin-RevId: 469238131

quiche/quic/core/quic_connection.cc

diff --git a/quiche/quic/core/quic_connection.cc b/quiche/quic/core/quic_connection.cc
index 7e780f2..6b0f592 100644
--- a/quiche/quic/core/quic_connection.cc
+++ b/quiche/quic/core/quic_connection.cc
@@ -4857,14 +4857,11 @@
       connection_->FlushCoalescedPacket();
     }
     connection_->FlushPackets();
-    if (GetQuicReloadableFlag(
-            quic_packet_flusher_check_connected_after_flush_packets)) {
-      QUIC_RELOADABLE_FLAG_COUNT(
-          quic_packet_flusher_check_connected_after_flush_packets);
-      if (!connection_->connected()) {
-        return;
-      }
+
+    if (!connection_->connected()) {
+      return;
     }
+
     if (!handshake_packet_sent_ && connection_->handshake_packet_sent_) {
       // This would cause INITIAL key to be dropped. Drop keys here to avoid
       // missing the write keys in the middle of writing.

quiche/quic/core/quic_connection_test.cc

diff --git a/quiche/quic/core/quic_connection_test.cc b/quiche/quic/core/quic_connection_test.cc
index dca0520..9f4e7c6 100644
--- a/quiche/quic/core/quic_connection_test.cc
+++ b/quiche/quic/core/quic_connection_test.cc
@@ -9899,11 +9899,6 @@
   use_tagging_decrypter();
 
   auto test_body = [&] {
-    if (!GetQuicReloadableFlag(
-            quic_packet_flusher_check_connected_after_flush_packets)) {
-      EXPECT_CALL(visitor_, OnHandshakePacketSent());
-    }
-
     EXPECT_CALL(visitor_,
                 OnConnectionClosed(_, ConnectionCloseSource::FROM_SELF))
         .WillOnce(Invoke(this, &QuicConnectionTest::SaveConnectionCloseFrame));

quiche/quic/core/quic_flags_list.h

diff --git a/quiche/quic/core/quic_flags_list.h b/quiche/quic/core/quic_flags_list.h
index 607a8fc..14b90a3 100644
--- a/quiche/quic/core/quic_flags_list.h
+++ b/quiche/quic/core/quic_flags_list.h
@@ -25,8 +25,6 @@
 QUIC_FLAG(quic_restart_flag_quic_disable_legacy_version_encapsulation, true)
 // If true, QUIC will default enable MTU discovery at server, with a target of 1450 bytes.
 QUIC_FLAG(quic_reloadable_flag_quic_enable_mtu_discovery_at_server, false)
-// If true, QuicConnection::ScopedPacketFlusher::~ScopedPacketFlusher will early return if connection is disconnected after FlushPackets.
-QUIC_FLAG(quic_reloadable_flag_quic_packet_flusher_check_connected_after_flush_packets, true)
 // If true, QuicGsoBatchWriter will support release time if it is available and the process has the permission to do so.
 QUIC_FLAG(quic_restart_flag_quic_support_release_time_for_gso, false)
 // If true, account added padding when coalesced packets get buffered.