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

chrome/browser/chromeos/cros/cryptohome_library.cc

 // 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.
 
 #include "chrome/browser/chromeos/cros/cryptohome_library.h"
 
 #include "base/message_loop.h"
 #include "chrome/browser/chrome_thread.h"
 
 namespace chromeos {
 
 bool CryptohomeLibraryImpl::CheckKey(const std::string& user_email,
                                      const std::string& passhash) {
   return chromeos::CryptohomeCheckKey(user_email.c_str(), passhash.c_str());
 }
 
 bool CryptohomeLibraryImpl::Mount(const std::string& user_email,
                                   const std::string& passhash) {
   return chromeos::CryptohomeMount(user_email.c_str(), passhash.c_str());
 }
 
 bool CryptohomeLibraryImpl::IsMounted() {
   return chromeos::CryptohomeIsMounted();
 }
 
+CryptohomeBlob CryptohomeLibraryImpl::GetSystemSalt() {
+  return chromeos::CryptohomeGetSystemSalt();
+}
+
 }  // namespace chromeos