Thread safe initialization of OSCrypt cache

components/os_crypt/os_crypt.h

 // Copyright 2014 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 COMPONENTS_OS_CRYPT_OS_CRYPT_H_
 #define COMPONENTS_OS_CRYPT_OS_CRYPT_H_
 
 #include <string>
 
 #include "base/macros.h"
@@ skipping 58 matching lines @@
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(OSCrypt);
 };
 
 #if defined(OS_LINUX) && !defined(OS_CHROMEOS) && defined(UNIT_TEST)
 // For unit testing purposes, inject methods to be used.
 // |get_key_storage_mock| provides the desired |KeyStorage| implementation.
 // If the provider returns |nullptr|, a hardcoded password will be used.
 // |get_password_v11_mock| provides a password to derive the encryption key from
-// If both parameters are |nullptr|, the real implementation is restored.
+// If one parameter is |nullptr|, the function will be not be replaced.
+// If all parameters are |nullptr|, the real implementation is restored.
 void UseMockKeyStorageForTesting(KeyStorageLinux* (*get_key_storage_mock)(),
                                  std::string* (*get_password_v11_mock)());
 #endif  // defined(OS_LINUX) && !defined(OS_CHROMEOS) && defined(UNIT_TEST)
 
 #endif  // COMPONENTS_OS_CRYPT_OS_CRYPT_H_