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

chrome/browser/chromeos/settings/device_settings_service.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_DEVICE_SETTINGS_SERVICE_H_
 #define CHROME_BROWSER_CHROMEOS_SETTINGS_DEVICE_SETTINGS_SERVICE_H_
 
 #include <deque>
 #include <string>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/callback.h"
 #include "base/compiler_specific.h"
 #include "base/memory/linked_ptr.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/observer_list.h"
 #include "chrome/browser/chromeos/policy/proto/chrome_device_policy.pb.h"
 #include "chromeos/dbus/session_manager_client.h"
 #include "components/ownership/owner_settings_service.h"
 #include "components/policy/core/common/cloud/cloud_policy_validator.h"
+#include "components/user_manager/user_id.h"
 #include "crypto/scoped_nss_types.h"
 #include "policy/proto/device_management_backend.pb.h"
 
 namespace crypto {
 class RSAPrivateKey;
 }
 
 namespace ownership {
 class OwnerKeyUtil;
 class PublicKey;
@@ skipping 120 matching lines @@
   // OwnerSettingsService.
   bool HasPrivateOwnerKey();
 
   // Sets the identity of the user that's interacting with the service. This is
   // relevant only for writing settings through SignAndStore().
   //
   // TODO (ygorshenin@, crbug.com/433840): get rid of the method when
   // write path for device settings will be removed from
   // DeviceSettingsProvider and all existing clients will be switched
   // to OwnerSettingsServiceChromeOS.
-  void InitOwner(const std::string& username,
+  void InitOwner(const user_manager::UserID& user_id,
                  const base::WeakPtr<ownership::OwnerSettingsService>&
                      owner_settings_service);
 
-  const std::string& GetUsername() const;
+  const user_manager::UserID& GetUserID() const;
 
   ownership::OwnerSettingsService* GetOwnerSettingsService() const;
 
   // Adds an observer.
   void AddObserver(Observer* observer);
   // Removes an observer.
   void RemoveObserver(Observer* observer);
 
   // SessionManagerClient::Observer:
   void OwnerKeySet(bool success) override;
@@ skipping 25 matching lines @@
   // Updates status and invokes the callback immediately.
   void HandleError(Status status, const base::Closure& callback);
 
   SessionManagerClient* session_manager_client_;
   scoped_refptr<ownership::OwnerKeyUtil> owner_key_util_;
 
   Status store_status_;
 
   std::vector<OwnershipStatusCallback> pending_ownership_status_callbacks_;
 
-  std::string username_;
+  user_manager::UserID user_id_;
   scoped_refptr<ownership::PublicKey> public_key_;
   base::WeakPtr<ownership::OwnerSettingsService> owner_settings_service_;
 
   scoped_ptr<enterprise_management::PolicyData> policy_data_;
   scoped_ptr<enterprise_management::ChromeDeviceSettingsProto> device_settings_;
 
   // The queue of pending operations. The first operation on the queue is
   // currently active; it gets removed and destroyed once it completes.
   std::deque<linked_ptr<SessionManagerOperation>> pending_operations_;
 
@@ skipping 14 matching lines @@
   ScopedTestDeviceSettingsService();
   ~ScopedTestDeviceSettingsService();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ScopedTestDeviceSettingsService);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_SETTINGS_DEVICE_SETTINGS_SERVICE_H_