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

net/quic/quic_flags.cc

Index: net/quic/quic_flags.cc
diff --git a/net/quic/quic_flags.cc b/net/quic/quic_flags.cc
index f9e9a7c68752ec24ff3946e5eebdd7b3f9a4cb11..fe7e452b9907a474035e9359592d53932c2877c1 100644
--- a/net/quic/quic_flags.cc
+++ b/net/quic/quic_flags.cc
@@ -138,3 +138,7 @@ 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;