Configure a SA host to use UACH for experiment.

Protected by QuicTag kGWCH.

PiperOrigin-RevId: 406451391

quic/core/crypto/crypto_protocol.h

diff --git a/quic/core/crypto/crypto_protocol.h b/quic/core/crypto/crypto_protocol.h
index efe830a..f0a20cc 100644
--- a/quic/core/crypto/crypto_protocol.h
+++ b/quic/core/crypto/crypto_protocol.h
@@ -425,6 +425,9 @@
                                                  // wire PING (ROWP) on the
                                                  // server side.
 
+// Client Hints triggers.
+const QuicTag kGWCH = TAG('G', 'W', 'C', 'H');
+
 // Rejection tags
 const QuicTag kRREJ = TAG('R', 'R', 'E', 'J');   // Reasons for server sending