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

chrome/browser/sync/sync_error_notifier_ash.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/sync/sync_error_notifier_ash.h"
 
 #include "ash/shell.h"
 #include "ash/shell_delegate.h"
 #include "ash/system/system_notifier.h"
 #include "base/strings/string16.h"
 #include "base/strings/utf_string_conversions.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/notifications/notification.h"
 #include "chrome/browser/notifications/notification_ui_manager.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/ash/multi_user/multi_user_util.h"
 #include "chrome/browser/ui/chrome_pages.h"
 #include "chrome/browser/ui/webui/signin/login_ui_service.h"
 #include "chrome/browser/ui/webui/signin/login_ui_service_factory.h"
 #include "chrome/common/url_constants.h"
 #include "chrome/grit/chromium_strings.h"
 #include "chrome/grit/generated_resources.h"
+#include "components/user_manager/user_id.h"
 #include "grit/theme_resources.h"
 #include "third_party/WebKit/public/web/WebTextDirection.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/base/resource/resource_bundle.h"
 #include "ui/message_center/notification.h"
 #include "ui/message_center/notification_delegate.h"
 
 #if defined(OS_CHROMEOS)
 #include "chrome/browser/chromeos/login/user_flow.h"
 #include "chrome/browser/chromeos/login/users/chrome_user_manager.h"
@@ skipping 126 matching lines @@
 
   // Set the delegate for the notification's sync setup button.
   SyncNotificationDelegate* delegate =
       new SyncNotificationDelegate(notification_id_, profile_);
 
   message_center::NotifierId notifier_id(
       message_center::NotifierId::SYSTEM_COMPONENT,
       kProfileSyncNotificationId);
 
   // Set |profile_id| for multi-user notification blocker.
-  notifier_id.profile_id = multi_user_util::GetUserIDFromProfile(profile_);
+  notifier_id.profile_id = multi_user_util::GetUserIDFromProfile(profile_).GetUserEmail();
 
   // Add a new notification.
   Notification notification(
       message_center::NOTIFICATION_TYPE_SIMPLE,
       GURL(notification_id_),
       l10n_util::GetStringUTF16(IDS_SYNC_ERROR_BUBBLE_VIEW_TITLE),
       l10n_util::GetStringUTF16(IDS_SYNC_PASSPHRASE_ERROR_BUBBLE_VIEW_MESSAGE),
       ui::ResourceBundle::GetSharedInstance().GetImageNamed(
           IDR_NOTIFICATION_ALERT),
       notifier_id,
       base::string16(),  // display_source
       notification_id_,
       data,
       delegate);
   notification_ui_manager->Add(notification, profile_);
 }