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

chrome/browser/ui/ash/launcher/chrome_launcher_controller.h

 // Copyright 2013 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_UI_ASH_LAUNCHER_CHROME_LAUNCHER_CONTROLLER_H_
 #define CHROME_BROWSER_UI_ASH_LAUNCHER_CHROME_LAUNCHER_CONTROLLER_H_
 
 #include <list>
 #include <map>
 #include <set>
@@ skipping 50 matching lines @@
 }
 
 namespace extensions {
 class Extension;
 }
 
 namespace ui {
 class BaseWindow;
 }
 
+namespace user_manager {
+class UserID;
+}
+
 // A list of the elements which makes up a simple menu description.
 typedef ScopedVector<ChromeLauncherAppMenuItem> ChromeLauncherAppMenuItems;
 
 // A class which needs to be overwritten dependent on the used OS to moitor
 // user switching.
 class ChromeLauncherControllerUserSwitchObserver {
  public:
   ChromeLauncherControllerUserSwitchObserver() {}
   virtual ~ChromeLauncherControllerUserSwitchObserver() {}
 
@@ skipping 265 matching lines @@
   // extensions::AppIconLoader:
   void SetAppImage(const std::string& app_id,
                    const gfx::ImageSkia& image) override;
 
   // ash::ShelfLayoutManagerObserver:
   void OnAutoHideBehaviorChanged(
       aura::Window* root_window,
       ash::ShelfAutoHideBehavior new_behavior) override;
 
   // Called when the active user has changed.
-  void ActiveUserChanged(const std::string& user_email);
+  void ActiveUserChanged(const user_manager::UserID& user_email);
 
   // Called when a user got added to the session.
   void AdditionalUserAddedToSession(Profile* profile);
 
   // Get the list of all running incarnations of this item.
   // |event_flags| specifies the flags which were set by the event which
   // triggered this menu generation. It can be used to generate different lists.
   ChromeLauncherAppMenuItems GetApplicationList(const ash::ShelfItem& item,
                                                 int event_flags);
 
@@ skipping 29 matching lines @@
   LauncherItemController* GetLauncherItemController(const ash::ShelfID id);
 
   // Returns true if |browser| is owned by the active user.
   bool IsBrowserFromActiveUser(Browser* browser);
 
   // Check if the shelf visibility (location, visibility) will change with a new
   // user profile or not. However, since the full visibility calculation of the
   // shelf cannot be performed here, this is only a probability used for
   // animation predictions.
   bool ShelfBoundsChangesProbablyWithUser(aura::Window* root_window,
-                                          const std::string& user_id) const;
+                                          const user_manager::UserID& user_id) const;
 
   // Access to the BrowserStatusMonitor for tests.
   BrowserStatusMonitor* browser_status_monitor_for_test() {
     return browser_status_monitor_.get();
   }
 
   // Access to the AppWindowLauncherController for tests.
   AppWindowLauncherController* app_window_controller_for_test() {
     return app_window_controller_.get();
   }
@@ skipping 20 matching lines @@
   friend class ShelfAppBrowserTest;
   friend class LauncherPlatformAppBrowserTest;
 
   typedef std::map<ash::ShelfID, LauncherItemController*> IDToItemControllerMap;
   typedef std::map<content::WebContents*, std::string> WebContentsToAppIDMap;
 
   // Remembers / restores list of running applications.
   // Note that this order will neither be stored in the preference nor will it
   // remember the order of closed applications since it is only temporary.
   void RememberUnpinnedRunningApplicationOrder();
-  void RestoreUnpinnedRunningApplicationOrder(const std::string& user_id);
+  void RestoreUnpinnedRunningApplicationOrder(const user_manager::UserID& user_id);
 
   // Creates a new app shortcut item and controller on the shelf at |index|.
   // Use kInsertItemAtEnd to add a shortcut as the last item.
   ash::ShelfID CreateAppShortcutLauncherItemWithType(
       const std::string& app_id,
       int index,
       ash::ShelfItemType shelf_item_type);
 
   // Invoked when the associated browser or app is closed.
   void LauncherItemClosed(ash::ShelfID id);
@@ skipping 145 matching lines @@
 
   // A special observer class to detect user switches.
   scoped_ptr<ChromeLauncherControllerUserSwitchObserver> user_switch_observer_;
 
   // If true, incoming pinned state changes should be ignored.
   bool ignore_persist_pinned_state_change_;
 
   // The list of running & un-pinned applications for different users on hidden
   // desktops.
   typedef std::vector<std::string> RunningAppListIds;
-  typedef std::map<std::string, RunningAppListIds> RunningAppListIdMap;
+  typedef std::map<user_manager::UserID, RunningAppListIds> RunningAppListIdMap;
   RunningAppListIdMap last_used_running_application_order_;
 
   DISALLOW_COPY_AND_ASSIGN(ChromeLauncherController);
 };
 
 #endif  // CHROME_BROWSER_UI_ASH_LAUNCHER_CHROME_LAUNCHER_CONTROLLER_H_