settings: Add async system salt retrieval logic in DeviceOAuth2TokenServiceFactory

chrome/browser/chromeos/settings/token_encryptor.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 CHROME_BROWSER_CHROMEOS_SETTINGS_TOKEN_ENCRYPTOR_H_
 #define CHROME_BROWSER_CHROMEOS_SETTINGS_TOKEN_ENCRYPTOR_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 15 matching lines @@
   // of the device).  Useful to avoid storing plain text in place like
   // Local State.
   virtual std::string EncryptWithSystemSalt(const std::string& token) = 0;
 
   // Decrypts |token| with the system salt key (stable for the lifetime
   // of the device).
   virtual std::string DecryptWithSystemSalt(
       const std::string& encrypted_token_hex) = 0;
 };
 
-// TokenEncryptor based on the cryptohome daemon. This implementation is used
-// in production.
+// TokenEncryptor based on the system salt from cryptohome daemon. This
+// implementation is used in production.
 class CryptohomeTokenEncryptor : public TokenEncryptor {
  public:
-  CryptohomeTokenEncryptor();
+  explicit CryptohomeTokenEncryptor(const std::string& system_salt);
   virtual ~CryptohomeTokenEncryptor();
 
   // TokenEncryptor overrides:
   virtual std::string EncryptWithSystemSalt(const std::string& token) OVERRIDE;
   virtual std::string DecryptWithSystemSalt(
       const std::string& encrypted_token_hex) OVERRIDE;
 
  private:
-  // Loads the system salt key based on the system salt from the cryptohome
-  // daemon. Returns true on success.
-  bool LoadSystemSaltKey();
-
   // Converts |passphrase| to a SymmetricKey using the given |salt|.
   crypto::SymmetricKey* PassphraseToKey(const std::string& passphrase,
                                         const std::string& salt);
 
   // Encrypts (AES) the token given |key| and |salt|.
   std::string EncryptTokenWithKey(crypto::SymmetricKey* key,
                                   const std::string& salt,
                                   const std::string& token);
 
   // Decrypts (AES) hex encoded encrypted token given |key| and |salt|.
   std::string DecryptTokenWithKey(crypto::SymmetricKey* key,
                                   const std::string& salt,
                                   const std::string& encrypted_token_hex);
 
-  // The cached system salt obtained from the cryptohome daemon.
+  // The cached system salt passed to the constructor, originally coming
+  // from cryptohome daemon.
   std::string system_salt_;
 
   // A key based on the system salt.  Useful for encrypting device-level
   // data for which we have no additional credentials.
   scoped_ptr<crypto::SymmetricKey> system_salt_key_;
 
   DISALLOW_COPY_AND_ASSIGN(CryptohomeTokenEncryptor);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_SETTINGS_TOKEN_ENCRYPTOR_H_