Add hook for extension to check sync status.

chrome/common/extensions/api/api.gyp

 # Copyright (c) 2012 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': 'api',
       'type': 'static_library',
       'sources': [
@@ skipping 11 matching lines @@
         # Only register the extension functions in extension system.
         'non_compiled_schema_files': [
           'adview.json',
           'browsing_data.json',
           'chromeos_info_private.json',
           'extension.json',
           'idltest.idl',
           'infobars.json',
           'media_player_private.json',
           'music_manager_private.idl',
-          'preferences_private.json',
           'principals_private.idl',
           'top_sites.json',
         ],
         'conditions': [
           ['OS!="android"', {
             'schema_files': [
               'activity_log_private.json',
               'alarms.idl',
               'app_current_window_internal.idl',
               'app_runtime.idl',
@@ skipping 41 matching lines @@
               'manifest_types.json',
               'mdns.idl',
               'media_galleries.idl',
               'media_galleries_private.idl',
               'metrics_private.json',
               'networking_private.json',
               'notifications.idl',
               'omnibox.json',
               'page_capture.json',
               'permissions.json',
+              'preferences_private.json',
               'power.idl',
               'push_messaging.idl',
               'runtime.json',
               'serial.idl',
               'sessions.json',
               'signed_in_devices.idl',
               'socket.idl',
               'sockets_tcp.idl',
               'sockets_tcp_server.idl',
               'sockets_udp.idl',
@@ skipping 79 matching lines @@
       'conditions': [
         ['chromeos==1', {
           'dependencies': [
             '<(DEPTH)/chrome/chrome.gyp:drive_proto',
           ],
         }],
       ],
     },
   ],
 }