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

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

Index: chrome/browser/ui/ash/launcher/chrome_launcher_controller.h
diff --git a/chrome/browser/ui/ash/launcher/chrome_launcher_controller.h b/chrome/browser/ui/ash/launcher/chrome_launcher_controller.h
index 6c30663bb706fd1b5e3c67832f1a0e5f276e1dcd..5a6c79ac21e10afad03ff16d23e037ea3cce1e53 100644
--- a/chrome/browser/ui/ash/launcher/chrome_launcher_controller.h
+++ b/chrome/browser/ui/ash/launcher/chrome_launcher_controller.h
@@ -68,6 +68,10 @@ 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;
 
@@ -353,7 +357,7 @@ class ChromeLauncherController : public ash::ShelfDelegate,
       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);
@@ -403,7 +407,7 @@ class ChromeLauncherController : public ash::ShelfDelegate,
   // 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() {
@@ -444,7 +448,7 @@ class ChromeLauncherController : public ash::ShelfDelegate,
   // 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.
@@ -610,7 +614,7 @@ class ChromeLauncherController : public ash::ShelfDelegate,
   // 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);