Disable QUIC v29 and earlier. Protected by FLAGS_quic_disable_pre_30.

net/quic/quic_protocol.cc

Index: net/quic/quic_protocol.cc
diff --git a/net/quic/quic_protocol.cc b/net/quic/quic_protocol.cc
index a784a2bcde80b7c8b7b492d2022526b713c7c4d3..e53db9cc00d7018e3b7cfdb50609ae976f91a2b3 100644
--- a/net/quic/quic_protocol.cc
+++ b/net/quic/quic_protocol.cc
@@ -179,6 +179,17 @@ QuicVersionVector QuicSupportedVersions() {
   return supported_versions;
 }
 
+QuicVersionVector FilterSupportedVersions(QuicVersionVector versions) {
+  QuicVersionVector filtered_versions(versions.size());
+  filtered_versions.clear();  // Guaranteed by spec not to change capacity.
+  for (QuicVersion version : versions) {
+    if (!FLAGS_quic_disable_pre_30 || version >= QUIC_VERSION_30) {
+      filtered_versions.push_back(version);
+    }
+  }
+  return filtered_versions;
+}
+
 QuicTag QuicVersionToQuicTag(const QuicVersion version) {
   switch (version) {
     case QUIC_VERSION_25: