Use GetSystemSalt from the cryptohome lib instead of reading salt off disk.

chrome/browser/chromeos/cros/cryptohome_library.h

 // Copyright (c) 2010 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_CROS_CRYPTOHOME_LIBRARY_H_
 #define CHROME_BROWSER_CHROMEOS_CROS_CRYPTOHOME_LIBRARY_H_
 
 #include <string>
 
 #include "base/singleton.h"
@@ skipping 13 matching lines @@
                      const std::string& passhash) = 0;
 
   // Asks cryptohomed to try to find the cryptohome for |user_email| and then
   // use |passhash| to unlock the key.
   virtual bool CheckKey(const std::string& user_email,
                         const std::string& passhash) = 0;
 
   // Asks cryptohomed if a drive is currently mounted.
   virtual bool IsMounted() = 0;
 
+  // Asks cryptohomed for the system salt.
+  virtual CryptohomeBlob GetSystemSalt() = 0;
+
 };
 
 // This class handles the interaction with the ChromeOS cryptohome library APIs.
 class CryptohomeLibraryImpl : public CryptohomeLibrary {
  public:
   CryptohomeLibraryImpl() {}
   virtual ~CryptohomeLibraryImpl() {}
 
   // CryptohomeLibrary overrides.
   virtual bool Mount(const std::string& user_email,
                      const std::string& passhash);
   virtual bool CheckKey(const std::string& user_email,
                         const std::string& passhash);
 
   // Asks cryptohomed if a drive is currently mounted.
   virtual bool IsMounted();
 
+  // Asks cryptohomed for the system salt.
+  virtual CryptohomeBlob GetSystemSalt();
+
  private:
   DISALLOW_COPY_AND_ASSIGN(CryptohomeLibraryImpl);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_CROS_CRYPTOHOME_LIBRARY_H_