Initialize the message center as part of the testing browser process

chrome/browser/notifications/notification_ui_manager_desktop.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/notification_ui_manager.h"
 
 #include <memory>
 #include <utility>
 
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/notifications/message_center_notification_manager.h"
 #include "chrome/browser/notifications/message_center_settings_controller.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/profiles/profile_manager.h"
 
 // static
 NotificationUIManager* NotificationUIManager::Create() {
   ProfileManager* profile_manager = g_browser_process->profile_manager();
   if (!profile_manager)
     return nullptr;
+  if (!g_browser_process->message_center())
+    return nullptr;
 
   std::unique_ptr<message_center::NotifierSettingsProvider> settings_provider(
       new MessageCenterSettingsController(
           profile_manager->GetProfileAttributesStorage()));
   return new MessageCenterNotificationManager(
       g_browser_process->message_center(),
       std::move(settings_provider));
 }