Introduce QUIC_VERSION_20: allowing endpoints to set different

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 9ad779861734cbb292d6043c669f1a2bb07896ac..398c94d525af96946218a3c4473ec3cf2bd19e05 100644
--- a/net/quic/quic_protocol.cc
+++ b/net/quic/quic_protocol.cc
@@ -169,6 +169,8 @@ QuicTag QuicVersionToQuicTag(const QuicVersion version) {
       return MakeQuicTag('Q', '0', '1', '8');
     case QUIC_VERSION_19:
       return MakeQuicTag('Q', '0', '1', '9');
+    case QUIC_VERSION_20:
+      return MakeQuicTag('Q', '0', '2', '0');
     default:
       // This shold be an ERROR because we should never attempt to convert an
       // invalid QuicVersion to be written to the wire.
@@ -200,6 +202,7 @@ string QuicVersionToString(const QuicVersion version) {
     RETURN_STRING_LITERAL(QUIC_VERSION_17);
     RETURN_STRING_LITERAL(QUIC_VERSION_18);
     RETURN_STRING_LITERAL(QUIC_VERSION_19);
+    RETURN_STRING_LITERAL(QUIC_VERSION_20);
     default:
       return "QUIC_VERSION_UNSUPPORTED";
   }