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

net/quic/crypto/proof_source.h

 // Copyright (c) 2013 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_PROOF_SOURCE_H_
 #define NET_QUIC_CRYPTO_PROOF_SOURCE_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 27 matching lines @@
   // expectation is that they will be cached forever.
   //
   // The signature values should be cached because |server_config| will be
   // somewhat static. However, since they aren't bounded, the ProofSource may
   // wish to evicit entries from that cache, thus the caller takes ownership of
   // |*out_signature|.
   //
   // |hostname| may be empty to signify that a default certificate should be
   // used.
   //
+  // |out_leaf_cert_sct| points to the signed timestamp (RFC6962) of the leaf
+  // cert.
   // This function may be called concurrently.
   virtual bool GetProof(const IPAddressNumber& server_ip,
                         const std::string& hostname,
                         const std::string& server_config,
                         bool ecdsa_ok,
                         const std::vector<std::string>** out_certs,
-                        std::string* out_signature) = 0;
+                        std::string* out_signature,
+                        std::string* out_leaf_cert_sct) = 0;
 };
 
 }  // namespace net
 
 #endif  // NET_QUIC_CRYPTO_PROOF_SOURCE_H_