We should use UserID object to identify users instead of username.

chrome/browser/chromeos/settings/cros_settings.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 CHROME_BROWSER_CHROMEOS_SETTINGS_CROS_SETTINGS_H_
 #define CHROME_BROWSER_CHROMEOS_SETTINGS_CROS_SETTINGS_H_
 
 #include <string>
 #include <vector>
 
 #include "base/callback_forward.h"
 #include "base/callback_list.h"
 #include "base/containers/hash_tables.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/threading/non_thread_safe.h"
 #include "chromeos/settings/cros_settings_names.h"
 #include "chromeos/settings/cros_settings_provider.h"
 
 namespace base {
 class DictionaryValue;
 class ListValue;
 class Value;
 }
 
+namespace user_manager {
+class UserID;
+}
+
 namespace chromeos {
 
 class DeviceSettingsService;
 
 // This class manages per-device/global settings.
 class CrosSettings : public base::NonThreadSafe {
  public:
   // Manage singleton instance.
   static void Initialize();
   static bool IsInitialized();
   static void Shutdown();
   static CrosSettings* Get();
 
   // Checks if the given username is whitelisted and allowed to sign-in to
   // this device. |wildcard_match| may be NULL. If it's present, it'll be set to
   // true if the whitelist check was satisfied via a wildcard.
-  static bool IsWhitelisted(const std::string& username, bool* wildcard_match);
+  static bool IsWhitelisted(const user_manager::UserID& user_id, bool* wildcard_match);
 
   // Creates a device settings service instance. This is meant for unit tests,
   // production code uses the singleton returned by Get() above.
   explicit CrosSettings(DeviceSettingsService* device_settings_service);
   virtual ~CrosSettings();
 
   // Helper function to test if the given |path| is a valid cros setting.
   static bool IsCrosSettings(const std::string& path);
 
   // Sets |in_value| to given |path| in cros settings.
@@ skipping 91 matching lines @@
   ScopedTestCrosSettings();
   ~ScopedTestCrosSettings();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ScopedTestCrosSettings);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_SETTINGS_CROS_SETTINGS_H_