Add support of serving SCT on the server side in QUIC, gated by QUIC_VERSION_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 5cca5434a3b64679e489ac42949b40a0305719dc..1e11c6ed30ea3f99e06b13cca4f18da0899c0960 100644
--- a/net/quic/quic_protocol.cc
+++ b/net/quic/quic_protocol.cc
@@ -144,6 +144,8 @@ QuicTag QuicVersionToQuicTag(const QuicVersion version) {
       return MakeQuicTag('Q', '0', '2', '8');
     case QUIC_VERSION_29:
       return MakeQuicTag('Q', '0', '2', '9');
+    case QUIC_VERSION_30:
+      return MakeQuicTag('Q', '0', '3', '0');
     default:
       // This shold be an ERROR because we should never attempt to convert an
       // invalid QuicVersion to be written to the wire.
@@ -175,6 +177,7 @@ string QuicVersionToString(const QuicVersion version) {
     RETURN_STRING_LITERAL(QUIC_VERSION_27);
     RETURN_STRING_LITERAL(QUIC_VERSION_28);
     RETURN_STRING_LITERAL(QUIC_VERSION_29);
+    RETURN_STRING_LITERAL(QUIC_VERSION_30);
     default:
       return "QUIC_VERSION_UNSUPPORTED";
   }