Add hook for extension to check sync status.

chrome/chrome_browser_extensions.gypi

 # Copyright (c) 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.
 
 {
   'targets': [
     {
       'target_name': 'browser_extensions',
       'type': 'static_library',
       'variables': { 'enable_wexit_time_destructors': 1, },
@@ skipping 396 matching lines @@
         'browser/extensions/api/preference/chrome_direct_setting.cc',
         'browser/extensions/api/preference/chrome_direct_setting.h',
         'browser/extensions/api/preference/chrome_direct_setting_api.cc',
         'browser/extensions/api/preference/chrome_direct_setting_api.h',
         'browser/extensions/api/preference/preference_api.cc',
         'browser/extensions/api/preference/preference_api.h',
         'browser/extensions/api/preference/preference_api_constants.cc',
         'browser/extensions/api/preference/preference_api_constants.h',
         'browser/extensions/api/preference/preference_helpers.cc',
         'browser/extensions/api/preference/preference_helpers.h',
+        'browser/extensions/api/preferences_private/preferences_private_api.h',
+        'browser/extensions/api/preferences_private/preferences_private_api.cc',
         'browser/extensions/api/principals_private/principals_private_api.cc',
         'browser/extensions/api/principals_private/principals_private_api.h',
         'browser/extensions/api/processes/processes_api.cc',
         'browser/extensions/api/processes/processes_api.h',
         'browser/extensions/api/processes/processes_api_constants.cc',
         'browser/extensions/api/processes/processes_api_constants.h',
         'browser/extensions/api/profile_keyed_api_factory.h',
         'browser/extensions/api/proxy/proxy_api.cc',
         'browser/extensions/api/proxy/proxy_api.h',
         'browser/extensions/api/proxy/proxy_api_constants.cc',
@@ skipping 799 matching lines @@
           'variables': {
             'proto_in_dir': 'browser/chromeos/contacts',
             'proto_out_dir': 'chrome/browser/chromeos/contacts',
           },
           'includes': [ '../build/protoc.gypi' ]
         },
       ],
     },],  # 'chromeos=1'
   ],  # 'conditions'
 }