Add new certificateProvider extension API.

net/ssl/ssl_platform_key.h

 // Copyright 2015 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_SSL_SSL_PLATFORM_KEY_H_
 #define NET_SSL_SSL_PLATFORM_KEY_H_
 
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
+#include "net/base/net_export.h"
 
 namespace base {
 class SequencedTaskRunner;
 }
 
 namespace net {
 
 class SSLPrivateKey;
 class X509Certificate;
 
+using FetchPrivateKeyFunc =
+    scoped_ptr<SSLPrivateKey>(X509Certificate* certificate);
+
+NET_EXPORT extern FetchPrivateKeyFunc* fetch_private_key_func;
+
 // Looks up the private key from the platform key store corresponding to
 // |certificate|'s public key and returns an SSLPrivateKey which offloads
 // signing operations to |task_runner|. |task_runner| is a SequencedTaskRunner
 // to allow for buggy third-party smartcard drivers.
 scoped_ptr<SSLPrivateKey> FetchClientCertPrivateKey(
     X509Certificate* certificate,
     scoped_refptr<base::SequencedTaskRunner> task_runner);
 
 }  // namespace net
 
 #endif  // NET_SSL_SSL_PLATFORM_KEY_H_