settings: Add async system salt retrieval logic in DeviceOAuth2TokenServiceFactory

chromeos/cryptohome/system_salt_getter.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 CHROMEOS_CRYPTOHOME_SYSTEM_SALT_GETTER_H_
 #define CHROMEOS_CRYPTOHOME_SYSTEM_SALT_GETTER_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 22 matching lines @@
   // Returns system hash in hex encoded ascii format. Note: this may return
   // an empty string (e.g. if cryptohome is not running). It is up to the
   // calling function to try again after a delay if desired.
   void GetSystemSalt(const GetSystemSaltCallback& callback);
 
   // Synchronous version of GetSystemSalt().
   // Blocks the UI thread until the Cryptohome service returns the result.
   // DEPRECATED: DO NOT USE.
   std::string GetSystemSaltSync();
 
-  // Returns system hash in hex encoded ascii format, cached by a prior call
-  // to GetSystemSalt(). Note: this may return an empty string (e.g. if
-  // GetSystemSalt() is not yet called).
-  std::string GetCachedSystemSalt();
-
  protected:
   SystemSaltGetter();
   ~SystemSaltGetter();
 
  private:
   // Used to implement GetSystemSalt().
   void GetSystemSaltInternal(const GetSystemSaltCallback& callback,
                              bool service_is_available);
 
   // Loads the system salt from cryptohome and caches it.
   void LoadSystemSalt();
 
   std::string system_salt_;
 
   base::WeakPtrFactory<SystemSaltGetter> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(SystemSaltGetter);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROMEOS_CRYPTOHOME_SYSTEM_SALT_GETTER_H_