Create new QUIC tags for Mentat testing

net/quic/core/crypto/crypto_protocol.h

Index: net/quic/core/crypto/crypto_protocol.h
diff --git a/net/quic/core/crypto/crypto_protocol.h b/net/quic/core/crypto/crypto_protocol.h
index cc3fdbfbab458aaf10421c38d36cd0fb70e1af50..50c382149b027915df599933bbece794be02fc69 100644
--- a/net/quic/core/crypto/crypto_protocol.h
+++ b/net/quic/core/crypto/crypto_protocol.h
@@ -130,6 +130,10 @@ const QuicTag kBWS2 = TAG('B', 'W', 'S', '2');  // Server bw resumption v2.
 const QuicTag kMTUH = TAG('M', 'T', 'U', 'H');  // High-target MTU discovery.
 const QuicTag kMTUL = TAG('M', 'T', 'U', 'L');  // Low-target MTU discovery.
 
+// Tags for async signing experiments
+const QuicTag kASYN = TAG('A', 'S', 'Y', 'N');  // Perform asynchronous signing
+const QuicTag kSYNC = TAG('S', 'Y', 'N', 'C');  // Perform synchronous signing
+
 const QuicTag kFHOL = TAG('F', 'H', 'O', 'L');   // Force head of line blocking.
 
 // Proof types (i.e. certificate types)