Refactor code that defers extension background page loading

extensions/extensions.gyp

 # Copyright 2013 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.
 
 {
   'variables': {
     'chromium_code': 1,
   },
   'targets': [
     {
@@ skipping 408 matching lines @@
         'browser/file_reader.cc',
         'browser/file_reader.h',
         'browser/lazy_background_task_queue.cc',
         'browser/lazy_background_task_queue.h',
         'browser/management_policy.cc',
         'browser/management_policy.h',
         'browser/pref_names.cc',
         'browser/pref_names.h',
         'browser/process_manager.cc',
         'browser/process_manager.h',
+        'browser/process_manager_delegate.h',
         'browser/process_manager_observer.h',
         'browser/process_map.cc',
         'browser/process_map.h',
         'browser/process_map_factory.cc',
         'browser/process_map_factory.h',
         'browser/quota_service.cc',
         'browser/quota_service.h',
         'browser/renderer_startup_helper.cc',
         'browser/renderer_startup_helper.h',
         'browser/runtime_data.cc',
@@ skipping 263 matching lines @@
         'test/test_extensions_client.cc',
         'test/test_extensions_client.h',
         'test/test_permission_message_provider.cc',
         'test/test_permission_message_provider.h',
         'test/test_permissions_provider.cc',
         'test/test_permissions_provider.h',
       ],
     },
   ]
 }