relnote: Adding FLAGS_require_handshake_confirmation to emergency-disable

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 5391673fd708ba3fc52b537cd066fea8ef5ac18d..0b42e62ebef3656c7705c1342d2e6a7d5471aaa6 100644
--- a/net/quic/crypto/quic_crypto_server_config.cc
+++ b/net/quic/crypto/quic_crypto_server_config.cc
@@ -1014,6 +1014,14 @@ void QuicCryptoServerConfig::EvaluateClientHello(
     helper.ValidationComplete(QUIC_NO_ERROR, "");
     return;
   }
+  // If we hit this block, the server nonce was empty.  If we're requiring
+  // handshake confirmation for DoS reasons and there's no server nonce present,
+  // reject the CHLO.
+  if (FLAGS_quic_require_handshake_confirmation) {
+    info->reject_reasons.push_back(SERVER_NONCE_REQUIRED_FAILURE);
+    helper.ValidationComplete(QUIC_NO_ERROR, "");
+    return;
+  }
 
   // We want to contact strike register only if there are no errors because it
   // is a RPC call and is expensive.