Disable QUIC versions 33 and earlier, protected by FLAGS_quic_disable_pre_34.

net/quic/core/quic_protocol.h

Index: net/quic/core/quic_protocol.h
diff --git a/net/quic/core/quic_protocol.h b/net/quic/core/quic_protocol.h
index 191883280f4d7e786e374e97b2485d125d0ddcf7..040e53029a32a635eb5f12008c2ffc690a715388 100644
--- a/net/quic/core/quic_protocol.h
+++ b/net/quic/core/quic_protocol.h
@@ -375,6 +375,9 @@ enum QuicVersion {
                          // header, uses new ack and stop waiting wire format.
   QUIC_VERSION_35 = 35,  // Allows endpoints to independently set stream limit.
   QUIC_VERSION_36 = 36,  // Add support to force HOL blocking.
+
+  // IMPORTANT: if you are adding to this std::list, follow the instructions at
+  // http://sites/quic/adding-and-removing-versions
 };
 
 // This vector contains QUIC versions which we currently support.
@@ -1395,6 +1398,8 @@ class NET_EXPORT_PRIVATE QuicVersionManager {
  private:
   // FLAGS_quic_disable_pre_32
   bool disable_pre_32_;
+  // FLAGS_quic_disable_pre_34
+  bool disable_pre_34_;
   // FLAGS_quic_enable_version_35
   bool enable_version_35_;
   // FLAGS_quic_enable_version_36_v2