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

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

Index: chrome/browser/ui/ash/launcher/multi_profile_app_window_launcher_controller.cc
diff --git a/chrome/browser/ui/ash/launcher/multi_profile_app_window_launcher_controller.cc b/chrome/browser/ui/ash/launcher/multi_profile_app_window_launcher_controller.cc
index 00e8c7379ed6a1c4c18ac5bd400f9cad9a12356a..5a389f64823a0bd40b6b1f09f635dec518e64ecd 100644
--- a/chrome/browser/ui/ash/launcher/multi_profile_app_window_launcher_controller.cc
+++ b/chrome/browser/ui/ash/launcher/multi_profile_app_window_launcher_controller.cc
@@ -36,7 +36,7 @@ MultiProfileAppWindowLauncherController::
 }
 
 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
@@ -147,7 +147,7 @@ bool MultiProfileAppWindowLauncherController::UserHasAppOnActiveDesktop(
   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();