Add the IDL and stub implementation for the chrome.passwordsPrivate API.

chrome/common/extensions/api/schemas.gypi

 # Copyright 2014 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.
 
 {
   'sources': [
     '<@(schema_files)',
   ],
   'variables': {
     'main_schema_files': [
@@ skipping 45 matching lines @@
       'launcher_page.idl',
       'location.idl',
       'manifest_types.json',
       'mdns.idl',
       'media_galleries.idl',
       'metrics_private.json',
       'notification_provider.idl',
       'notifications.idl',
       'omnibox.json',
       'page_capture.json',
+      'passwords_private.idl',
       'permissions.json',
       'preferences_private.json',
       'reading_list_private.json',
       'screenlock_private.idl',
       'search_engines_private.idl',
       'sessions.json',
       'settings_private.idl',
       'signed_in_devices.idl',
       'streams_private.idl',
       'sync_file_system.idl',
@@ skipping 87 matching lines @@
         'schema_files': [
           '<@(webrtc_schema_files)',
         ],
       }],
     ],
     'cc_dir': 'chrome/common/extensions/api',
     'root_namespace': 'extensions::api::%(namespace)s',
     'impl_dir_': 'chrome/browser/extensions/api',
   },
 }