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

chrome/browser/ui/ash/launcher/multi_profile_app_window_launcher_controller.cc

 // Copyright 2014 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/ui/ash/launcher/multi_profile_app_window_launcher_controller.h"
 
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/profiles/profile_manager.h"
 #include "chrome/browser/ui/ash/multi_user/multi_user_util.h"
 #include "chrome/browser/ui/ash/multi_user/multi_user_window_manager.h"
@@ skipping 18 matching lines @@
 MultiProfileAppWindowLauncherController::
     ~MultiProfileAppWindowLauncherController() {
   // We need to remove all Registry observers for added users.
   for (AppWindowRegistryList::iterator it = multi_user_registry_.begin();
        it != multi_user_registry_.end();
        ++it)
     (*it)->RemoveObserver(this);
 }
 
 void MultiProfileAppWindowLauncherController::ActiveUserChanged(
-    const std::string& user_email) {
+    const user_manager::UserID& user_id) {
   // The active user has changed and we need to traverse our list of items to
   // show / hide them one by one. To avoid that a user dependent state
   // "survives" in a launcher item, we first delete all items making sure that
   // nothing remains and then re-create them again.
   for (AppWindowList::iterator it = app_window_list_.begin();
        it != app_window_list_.end();
        ++it) {
     extensions::AppWindow* app_window = *it;
     Profile* profile =
         Profile::FromBrowserContext(app_window->browser_context());
@@ skipping 90 matching lines @@
       std::find(app_window_list_.begin(), app_window_list_.end(), app_window);
   DCHECK(it != app_window_list_.end());
   app_window_list_.erase(it);
 }
 
 bool MultiProfileAppWindowLauncherController::UserHasAppOnActiveDesktop(
     extensions::AppWindow* app_window) {
   const std::string& app_id = app_window->extension_id();
   content::BrowserContext* app_context = app_window->browser_context();
   DCHECK(!app_context->IsOffTheRecord());
-  const std::string& current_user = multi_user_util::GetCurrentUserId();
+  const user_manager::UserID& current_user = multi_user_util::GetCurrentUserId();
   chrome::MultiUserWindowManager* manager =
       chrome::MultiUserWindowManager::GetInstance();
   for (AppWindowList::iterator it = app_window_list_.begin();
        it != app_window_list_.end();
        ++it) {
     extensions::AppWindow* other_window = *it;
     DCHECK(!other_window->browser_context()->IsOffTheRecord());
     if (manager->IsWindowOnDesktopOfUser(other_window->GetNativeWindow(),
                                          current_user) &&
         app_id == other_window->extension_id() &&
         app_context == other_window->browser_context()) {
       return true;
     }
   }
   return false;
 }