Add chrome.usbPrivate API for use by USB device WEBUI.

extensions/common/api/api.gyp

 # 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.
 
 {
   'targets': [
     {
       # GN version: //extensions/common/api
       'target_name': 'extensions_api',
       'type': 'static_library',
@@ skipping 23 matching lines @@
               'power.idl',
               'runtime.json',
               'serial.idl',
               'socket.idl',
               'sockets_tcp.idl',
               'sockets_tcp_server.idl',
               'sockets_udp.idl',
               'storage.json',
               'test.json',
               'usb.idl',
+              'usb_private.idl',
             ],
           }, {
             # TODO: Eliminate these on Android. See crbug.com/305852.
             'schema_files': [
               'runtime.json',
             ],
           }],
         ],
         'cc_dir': 'extensions/common/api',
         'root_namespace': 'extensions::core_api::%(namespace)s',
         'impl_dir': 'extensions/browser/api',
       },
       'conditions': [
         ['enable_extensions==1', {
           'dependencies': [
             '<(DEPTH)/device/serial/serial.gyp:device_serial',
             '<(DEPTH)/skia/skia.gyp:skia',
           ],
         }],
       ],
     },
   ],
 }