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

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

Index: chrome/browser/ui/ash/launcher/chrome_launcher_controller.cc
diff --git a/chrome/browser/ui/ash/launcher/chrome_launcher_controller.cc b/chrome/browser/ui/ash/launcher/chrome_launcher_controller.cc
index 0e6b955ca7a33a7ad24c4ca7b359b655f1ffe04c..b0fe448519ea5c10fb0c0cc4add3ac79e85eba18 100644
--- a/chrome/browser/ui/ash/launcher/chrome_launcher_controller.cc
+++ b/chrome/browser/ui/ash/launcher/chrome_launcher_controller.cc
@@ -67,6 +67,7 @@
 #include "chrome/common/url_constants.h"
 #include "chrome/grit/generated_resources.h"
 #include "components/favicon/content/content_favicon_driver.h"
+#include "components/user_manager/user_id.h"
 #include "content/public/browser/navigation_entry.h"
 #include "content/public/browser/notification_registrar.h"
 #include "content/public/browser/notification_service.h"
@@ -315,7 +316,7 @@ class ChromeLauncherControllerUserSwitchObserverChromeOS
 
   // Users which were just added to the system, but which profiles were not yet
   // (fully) loaded.
-  std::set<std::string> added_user_ids_waiting_for_profiles_;
+  std::set<user_manager::UserID> added_user_ids_waiting_for_profiles_;
 
   DISALLOW_COPY_AND_ASSIGN(ChromeLauncherControllerUserSwitchObserverChromeOS);
 };
@@ -323,11 +324,11 @@ class ChromeLauncherControllerUserSwitchObserverChromeOS
 void ChromeLauncherControllerUserSwitchObserverChromeOS::UserAddedToSession(
     const user_manager::User* active_user) {
   Profile* profile = multi_user_util::GetProfileFromUserID(
-      active_user->email());
+      active_user->GetUserID());
   // If we do not have a profile yet, we postpone forwarding the notification
   // until it is loaded.
   if (!profile)
-    added_user_ids_waiting_for_profiles_.insert(active_user->email());
+    added_user_ids_waiting_for_profiles_.insert(active_user->GetUserID());
   else
     AddUser(profile);
 }
@@ -340,8 +341,8 @@ void ChromeLauncherControllerUserSwitchObserverChromeOS::Observe(
       !added_user_ids_waiting_for_profiles_.empty()) {
     // Check if the profile is from a user which was on the waiting list.
     Profile* profile = content::Source<Profile>(source).ptr();
-    std::string user_id = multi_user_util::GetUserIDFromProfile(profile);
-    std::set<std::string>::iterator it = std::find(
+    user_manager::UserID user_id = multi_user_util::GetUserIDFromProfile(profile);
+    std::set<user_manager::UserID>::iterator it = std::find(
         added_user_ids_waiting_for_profiles_.begin(),
         added_user_ids_waiting_for_profiles_.end(),
         user_id);
@@ -1100,7 +1101,7 @@ ChromeLauncherController::ActivateWindowOrMinimizeIfActive(
   if (chrome::MultiUserWindowManager::GetMultiProfileMode() ==
           chrome::MultiUserWindowManager::MULTI_PROFILE_MODE_SEPARATED) {
     aura::Window* native_window = window->GetNativeWindow();
-    const std::string& current_user =
+    const user_manager::UserID& current_user =
         multi_user_util::GetUserIDFromProfile(profile());
     chrome::MultiUserWindowManager* manager =
         chrome::MultiUserWindowManager::GetInstance();
@@ -1180,7 +1181,7 @@ void ChromeLauncherController::ShelfStatusChanged() {
 }
 
 void ChromeLauncherController::ActiveUserChanged(
-    const std::string& user_email) {
+    const user_manager::UserID& user_id) {
   // Store the order of running applications for the user which gets inactive.
   RememberUnpinnedRunningApplicationOrder();
   // Coming here the default profile is already switched. All profile specific
@@ -1190,9 +1191,9 @@ void ChromeLauncherController::ActiveUserChanged(
   // set it as active.
   AttachProfile(ProfileManager::GetActiveUserProfile());
   // Update the V1 applications.
-  browser_status_monitor_->ActiveUserChanged(user_email);
+  browser_status_monitor_->ActiveUserChanged(user_id);
   // Switch the running applications to the new user.
-  app_window_controller_->ActiveUserChanged(user_email);
+  app_window_controller_->ActiveUserChanged(user_id);
   // Update the user specific shell properties from the new user profile.
   UpdateAppLaunchersFromPref();
   SetShelfAlignmentFromPrefs();
@@ -1203,7 +1204,7 @@ void ChromeLauncherController::ActiveUserChanged(
 #endif  // defined(OS_CHROMEOS)
   // Restore the order of running, but unpinned applications for the activated
   // user.
-  RestoreUnpinnedRunningApplicationOrder(user_email);
+  RestoreUnpinnedRunningApplicationOrder(user_id);
   // Inform the system tray of the change.
   ash::Shell::GetInstance()->system_tray_delegate()->ActiveUserWasChanged();
   // Force on-screen keyboard to reset.
@@ -1453,7 +1454,7 @@ void ChromeLauncherController::RememberUnpinnedRunningApplicationOrder() {
 }
 
 void ChromeLauncherController::RestoreUnpinnedRunningApplicationOrder(
-    const std::string& user_id) {
+    const user_manager::UserID& user_id) {
   const RunningAppListIdMap::iterator app_id_list =
       last_used_running_application_order_.find(user_id);
   if (app_id_list == last_used_running_application_order_.end())
@@ -1506,7 +1507,7 @@ bool ChromeLauncherController::IsBrowserFromActiveUser(Browser* browser) {
 
 bool ChromeLauncherController::ShelfBoundsChangesProbablyWithUser(
     aura::Window* root_window,
-    const std::string& user_id) const {
+    const user_manager::UserID& user_id) const {
   Profile* other_profile = multi_user_util::GetProfileFromUserID(user_id);
   DCHECK_NE(other_profile, profile_);