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

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 913 matching lines @@
             'browser/extensions/api/input_ime/input_ime_api.cc',
             'browser/extensions/api/input_ime/input_ime_api.h',
             'browser/extensions/api/log_private/filter_handler.cc',
             'browser/extensions/api/log_private/filter_handler.h',
             'browser/extensions/api/log_private/log_parser.cc',
             'browser/extensions/api/log_private/log_parser.h',
             'browser/extensions/api/log_private/log_private_api.h',
             'browser/extensions/api/log_private/log_private_api_chromeos.cc',
             'browser/extensions/api/log_private/syslog_parser.cc',
             'browser/extensions/api/log_private/syslog_parser.h',
+            'browser/chromeos/extensions/screenlock_private_api.cc',
+            'browser/chromeos/extensions/screenlock_private_api.h',
             'browser/extensions/api/terminal/terminal_extension_helper.cc',
             'browser/extensions/api/terminal/terminal_extension_helper.h',
             'browser/extensions/api/terminal/terminal_private_api.cc',
             'browser/extensions/api/terminal/terminal_private_api.h',
           ],
         }],
         ['use_ash==1', {
           'sources': [
             'browser/extensions/api/tabs/ash_panel_contents.cc',
             'browser/extensions/api/tabs/ash_panel_contents.h',
@@ skipping 242 matching lines @@
           'variables': {
             'proto_in_dir': 'browser/chromeos/contacts',
             'proto_out_dir': 'chrome/browser/chromeos/contacts',
           },
           'includes': [ '../build/protoc.gypi' ]
         },
       ],
     },],  # 'chromeos=1'
   ],  # 'conditions'
 }