Support WebTransport negotiation in HTTP/3.

PiperOrigin-RevId: 360499528
Change-Id: I1ca3ee42d10991704994f14fb009a56b91e3e63c
diff --git a/quic/core/http/http_constants.h b/quic/core/http/http_constants.h
index 9757e72..a5409b5 100644
--- a/quic/core/http/http_constants.h
+++ b/quic/core/http/http_constants.h
@@ -38,6 +38,8 @@
   SETTINGS_QPACK_BLOCKED_STREAMS = 0x07,
   // draft-ietf-masque-h3-datagram.
   SETTINGS_H3_DATAGRAM = 0x276,
+  // draft-ietf-webtrans-http3-00
+  SETTINGS_WEBTRANS_DRAFT00 = 0x2b603742,
 };
 
 // Returns HTTP/3 SETTINGS identifier as a string.