Initialize the message center as part of the testing browser process

ash/test/BUILD.gn

 # Copyright 2016 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/ui.gni")
 
 # Used to test ash with an aura backend.
 source_set("ash_with_aura_test_support") {
   testonly = true
   sources = [
@@ skipping 190 matching lines @@
     "ash_interactive_ui_test_base.h",
   ]
   deps = [
     ":test_support_with_content",
     "//base",
     "//skia",
     "//testing/gtest",
     "//ui/aura",
     "//ui/base",
     "//ui/gl:test_support",
+    "//ui/message_center:message_center",
   ]
 }