Add support of serving SCT on the server side in QUIC, gated by QUIC_VERSION_30.

net/quic/crypto/crypto_protocol.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_QUIC_CRYPTO_CRYPTO_PROTOCOL_H_
 #define NET_QUIC_CRYPTO_CRYPTO_PROTOCOL_H_
 
 #include <string>
 
 #include "net/base/net_export.h"
@@ skipping 170 matching lines @@
 // Likewise tags with random values should be towards the beginning of the
 // message because the server mightn't hold state for a rejected client hello
 // and therefore the client may have issues reassembling the rejection message
 // in the event that it sent two client hellos.
 const QuicTag kServerNonceTag =
     TAG('S', 'N', 'O', 0);  // The server's nonce
 const QuicTag kSourceAddressTokenTag =
     TAG('S', 'T', 'K', 0);  // Source-address token
 const QuicTag kCertificateTag =
     TAG('C', 'R', 'T', 255);  // Certificate chain
+const QuicTag kCertificateSCTTag =
+    TAG('C', 'S', 'C', 'T');  // Signed cert timestamp (RFC6962) of leaf cert.
 
 #undef TAG
 
 const size_t kMaxEntries = 128;  // Max number of entries in a message.
 
 const size_t kNonceSize = 32;  // Size in bytes of the connection nonce.
 
 const size_t kOrbitSize = 8;  // Number of bytes in an orbit value.
 
 // kProofSignatureLabel is prepended to server configs before signing to avoid
 // any cross-protocol attacks on the signature.
 const char kProofSignatureLabel[] = "QUIC server config signature";
 
 // kClientHelloMinimumSize is the minimum size of a client hello. Client hellos
 // will have PAD tags added in order to ensure this minimum is met and client
 // hellos smaller than this will be an error. This minimum size reduces the
 // amplification factor of any mirror DoS attack.
 //
 // A client may pad an inchoate client hello to a size larger than
 // kClientHelloMinimumSize to make it more likely to receive a complete
 // rejection message.
 const size_t kClientHelloMinimumSize = 1024;
 
 }  // namespace net
 
 #endif  // NET_QUIC_CRYPTO_CRYPTO_PROTOCOL_H_