Add private system extension API to get system update status

chrome/chrome_tests.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.
 {
   'variables' : {
     # Variables for js2gtest rules
     'gypv8sh': '../tools/gypv8sh.py',
     'js2gtest': 'test/base/js2gtest.js',
     'mock_js': 'third_party/mock4js/mock4js.js',
     'test_api_js': 'test/data/webui/test_api.js',
@@ skipping 2428 matching lines @@
         'browser/accessibility/renderer_accessibility_browsertest.cc',
         'browser/autocomplete/autocomplete_browsertest.cc',
         'browser/autofill/form_structure_browsertest.cc',
         'browser/automation/automation_tab_helper_browsertest.cc',
         'browser/bookmarks/bookmark_extension_apitest.cc',
         'browser/bookmarks/bookmark_manager_extension_apitest.cc',
         'browser/browsing_data_database_helper_browsertest.cc',
         'browser/browsing_data_helper_browsertest.h',
         'browser/browsing_data_indexed_db_helper_browsertest.cc',
         'browser/browsing_data_local_storage_helper_browsertest.cc',
+        'browser/chromeos/accessibility/accessibility_private_extension_apitest.cc',
         'browser/chromeos/brightness_bubble_browsertest.cc',
         'browser/chromeos/cros/cros_in_process_browser_test.cc',
         'browser/chromeos/cros/cros_in_process_browser_test.h',
         'browser/chromeos/cros/cros_mock.cc',
         'browser/chromeos/cros/cros_mock.h',
         'browser/chromeos/cros/mock_screen_lock_library.cc',
         'browser/chromeos/cros/mock_screen_lock_library.h',
         'browser/chromeos/disks/mock_disk_mount_manager.cc',
         'browser/chromeos/disks/mock_disk_mount_manager.h',
         'browser/chromeos/extensions/file_browser_notifications_browsertest.cc',
@@ skipping 1857 matching lines @@
               # Use outputs of this action as inputs for the main target build.
               # Seems as a misnomer but makes this happy on Linux (scons).
               'process_outputs_as_sources': 1,
             },
           ],  # 'actions'
         },
       ]
     }],  # 'coverage!=0'
   ],  # 'conditions'
 }