The chrome.screenlockPrivate API allows select apps to control the ChromeOS ScreenLocker.

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 138 matching lines @@
                 'web_navigation.json',
                 'web_request.json',
                 'windows.json',
               ],
           }],
           ['chromeos==1', {
             'schema_files': [
               'diagnostics.idl',
               'file_browser_handler_internal.json',
               'log_private.idl',
+              'screenlock_private.idl',
               'wallpaper.json',
               'wallpaper_private.json',
             ],
           }],
           ['enable_webrtc==1', {
             'schema_files': [
               'webrtc_cast_send_transport.idl',
               'webrtc_cast_udp_transport.idl',
               'webrtc_logging_private.idl',
             ],
           }],
         ],
         'cc_dir': 'chrome/common/extensions/api',
         'root_namespace': 'extensions::api',
       },
       'dependencies': [
         '<(DEPTH)/skia/skia.gyp:skia',
         '<(DEPTH)/sync/sync.gyp:sync',
       ],
       'conditions': [
         ['chromeos==1', {
           'dependencies': [
             '<(DEPTH)/chrome/chrome.gyp:drive_proto',
           ],
         }],
       ],
     },
   ],
 }