Add a new flag to require QUIC handshake confirmation, but only for versions before 33 FLAGS_quic_r…

net/quic/quic_flags.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/quic/quic_flags.h"
 
 // If true, it will return as soon as an error is detected while validating
 // CHLO.
 bool FLAGS_use_early_return_when_verifying_chlo = true;
 
@@ skipping 120 matching lines @@
 // If true, use async codepaths to invoke ProofSource::GetProof.
 bool FLAGS_enable_async_get_proof = false;
 
 // If true, neuter null encrypted packets before sending the next handshake
 // message.
 bool FLAGS_quic_neuter_unencrypted_when_sending = false;
 
 // If true, QuicAlarm::Update will call a faster UpdateImpl implementation
 // instead of canceling and reregistering the alarm.
 bool FLAGS_quic_change_alarms_efficiently = false;
+
+// If true, requires handshake confirmations for all QUIC handshakes with
+// versions less than 33.
+bool FLAGS_quic_require_handshake_confirmation_pre33 = false;