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

chrome/browser/notifications/profile_notification.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/notifications/profile_notification.h"
 
 #include "base/strings/stringprintf.h"
 #include "chrome/browser/ui/ash/multi_user/multi_user_util.h"
+#include "components/user_manager/user_id.h"
 
 // static
 std::string ProfileNotification::GetProfileNotificationId(
     const std::string& delegate_id,
     ProfileID profile_id) {
   DCHECK(profile_id);
   return base::StringPrintf("notification-ui-manager#%p#%s",
                             profile_id,  // Each profile has its unique instance
                                          // including incognito profile.
                             delegate_id.c_str());
 }
 
 ProfileNotification::ProfileNotification(
     Profile* profile,
     const Notification& notification)
     : profile_(profile),
       notification_(
           // Uses Notification's copy constructor to assign the message center
           // id, which should be unique for every profile + Notification pair.
           GetProfileNotificationId(
               notification.delegate_id(),
               NotificationUIManager::GetProfileID(profile)),
           notification) {
   DCHECK(profile);
 #if defined(OS_CHROMEOS)
-  notification_.set_profile_id(multi_user_util::GetUserIDFromProfile(profile));
+  notification_.set_profile_id(multi_user_util::GetUserIDFromProfile(profile).GetUserEmail());
 #endif
 }
 
 ProfileNotification::~ProfileNotification() {}