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

chrome/browser/chromeos/settings/device_settings_service.cc

 // 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.
 
 #include "chrome/browser/chromeos/settings/device_settings_service.h"
 
 #include "base/bind.h"
 #include "base/logging.h"
 #include "base/message_loop/message_loop.h"
 #include "base/stl_util.h"
@@ skipping 53 matching lines @@
 
 // static
 DeviceSettingsService* DeviceSettingsService::Get() {
   CHECK(g_device_settings_service);
   return g_device_settings_service;
 }
 
 DeviceSettingsService::DeviceSettingsService()
     : session_manager_client_(NULL),
       store_status_(STORE_SUCCESS),
+      user_id_(std::string(), std::string()),
       load_retries_left_(kMaxLoadRetries),
       weak_factory_(this) {
 }
 
 DeviceSettingsService::~DeviceSettingsService() {
   DCHECK(pending_operations_.empty());
   FOR_EACH_OBSERVER(Observer, observers_, OnDeviceSettingsServiceShutdown());
 }
 
 void DeviceSettingsService::SetSessionManager(
@@ skipping 59 matching lines @@
     if (pending_operations_.empty())
       EnqueueLoad(false);
   }
 }
 
 bool DeviceSettingsService::HasPrivateOwnerKey() {
   return owner_settings_service_ && owner_settings_service_->IsOwner();
 }
 
 void DeviceSettingsService::InitOwner(
-    const std::string& username,
+    const user_manager::UserID& user_id,
     const base::WeakPtr<ownership::OwnerSettingsService>&
         owner_settings_service) {
-  // When InitOwner() is called twice with the same |username| it's
+  // When InitOwner() is called twice with the same |user_id| it's
   // worth to reload settings since owner key may become available.
-  if (!username_.empty() && username_ != username)
+  if (!user_id_.empty() && user_id_ != user_id)
     return;
-  username_ = username;
+  user_id_ = user_id;
   owner_settings_service_ = owner_settings_service;
 
   EnsureReload(true);
 }
 
-const std::string& DeviceSettingsService::GetUsername() const {
-  return username_;
+const user_manager::UserID& DeviceSettingsService::GetUserID() const {
+  return user_id_;
 }
 
 ownership::OwnerSettingsService*
 DeviceSettingsService::GetOwnerSettingsService() const {
   return owner_settings_service_.get();
 }
 
 void DeviceSettingsService::AddObserver(Observer* observer) {
   observers_.AddObserver(observer);
 }
@@ skipping 145 matching lines @@
   DeviceSettingsService::Initialize();
 }
 
 ScopedTestDeviceSettingsService::~ScopedTestDeviceSettingsService() {
   // Clean pending operations.
   DeviceSettingsService::Get()->UnsetSessionManager();
   DeviceSettingsService::Shutdown();
 }
 
 }  // namespace chromeos