relnote: Disables strike register lookups when talking QUIC_VERSION_27

net/quic/crypto/quic_crypto_server_config.cc

Index: net/quic/crypto/quic_crypto_server_config.cc
diff --git a/net/quic/crypto/quic_crypto_server_config.cc b/net/quic/crypto/quic_crypto_server_config.cc
index a4f28d959fbeef6f9ecf19ae44ecaf7fea2f97bf..173e98080920e548f39e9ba7d5ce881b973819b7 100644
--- a/net/quic/crypto/quic_crypto_server_config.cc
+++ b/net/quic/crypto/quic_crypto_server_config.cc
@@ -1040,13 +1040,27 @@ void QuicCryptoServerConfig::EvaluateClientHello(
     found_error = true;
   }
 
+  // Server nonce is optional, and used for key derivation if present.
+  client_hello.GetStringPiece(kServerNonceTag, &info->server_nonce);
+
+  if (version > QUIC_VERSION_26) {
+    DVLOG(1) << "No 0-RTT replay protection in QUIC_VERSION_27 and higher.";
+    // If the server nonce is empty and we're requiring handshake confirmation
+    // for DoS reasons then we must reject the CHLO.
+    if (FLAGS_quic_require_handshake_confirmation &&
+        info->server_nonce.empty()) {
+      info->reject_reasons.push_back(SERVER_NONCE_REQUIRED_FAILURE);
+    }
+    helper.ValidationComplete(QUIC_NO_ERROR, "");
+    return;
+  }
+
   if (!replay_protection_) {
     DVLOG(1) << "No replay protection.";
     helper.ValidationComplete(QUIC_NO_ERROR, "");
     return;
   }
 
-  client_hello.GetStringPiece(kServerNonceTag, &info->server_nonce);
   if (!info->server_nonce.empty()) {
     // If the server nonce is present, use it to establish uniqueness.
     HandshakeFailureReason server_nonce_error =