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

net/quic/crypto/proof_source_chromium.h

 // Copyright 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_CHROMIUM_H_
 #define NET_QUIC_CRYPTO_PROOF_SOURCE_CHROMIUM_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 18 matching lines @@
   // and the PKCS#8 RSA private key in |key_path|.
   bool Initialize(const base::FilePath& cert_path,
                   const base::FilePath& key_path);
 
   // ProofSource interface
   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) override;
+                std::string* out_signature,
+                std::string* out_leaf_cert_sct) override;
 
  private:
   scoped_ptr<crypto::RSAPrivateKey> private_key_;
   std::vector<std::string> certificates_;
 
   DISALLOW_COPY_AND_ASSIGN(ProofSourceChromium);
 };
 
 }  // namespace net
 
 #endif  // NET_QUIC_CRYPTO_PROOF_SOURCE_CHROMIUM_H_