Set up content in-process main threads via factory

content/content_utility.gypi

 # Copyright (c) 2011 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.
 
 {
   'dependencies': [
     '../base/base.gyp:base',
   ],
   'sources': [
     'public/utility/content_utility_client.cc',
     'public/utility/content_utility_client.h',
     'public/utility/utility_thread.cc',
     'public/utility/utility_thread.h',
     'utility/utility_main.cc',
+    'utility/utility_main_thread.cc',
+    'utility/utility_main_thread.h',
     'utility/utility_thread_impl.cc',
     'utility/utility_thread_impl.h',
   ],
   'include_dirs': [
     '..',
   ],
 }