Create a stub NSUserNotificationCenter and make tests use it.

chrome/test/BUILD.gn

 # 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.
 
 import("//build/config/chrome_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//chrome/common/features.gni")
@@ skipping 4125 matching lines @@
     ]
   }
   if (enable_notifications) {
     sources += [
       "../browser/notifications/desktop_notification_profile_util_unittest.cc",
       "../browser/notifications/message_center_notifications_unittest.cc",
       "../browser/notifications/message_center_settings_controller_unittest.cc",
       "../browser/notifications/notification_permission_context_unittest.cc",
       "../browser/notifications/notification_platform_bridge_mac_unittest.mm",
       "../browser/notifications/platform_notification_service_unittest.cc",
+      "../browser/notifications/stub_notification_center_mac.h",
+      "../browser/notifications/stub_notification_center_mac.mm",
     ]
     if (is_android) {
       sources -= [
         # Android does not use the Message Center notification system.
         "../browser/notifications/message_center_notifications_unittest.cc",
         "../browser/notifications/message_center_settings_controller_unittest.cc",
       ]
     }
   }
 
@@ skipping 882 matching lines @@
       "touch_hud",
       "ui",
     ]
 
     if (is_linux && !is_android) {
       deps += [ "//components/font_service:manifest" ]
       packaged_services += [ "font_service" ]
     }
   }
 }