Disable QUIC versions less than v32, protected by --FLAGS_quic_disable_pre_32.

net/quic/core/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/core/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 144 matching lines @@
 // If true, defer creation of new connection till its CHLO arrives.
 bool FLAGS_quic_buffer_packet_till_chlo = false;
 
 // If true, the connection will check whether it is application-limited, and
 // notify the congestion controller about it.
 bool FLAGS_quic_enable_app_limited_check = true;
 
 // Deprecate QuicPacketCreator::next_packet_number_length_ because it's no
 // longer necessary.
 bool FLAGS_quic_simple_packet_number_length_2 = true;
+
+// If true, disables QUIC version less than 32.
+bool FLAGS_quic_disable_pre_32 = true;