Adding tests for USB extension API

chrome/chrome_tests.gypi

 # 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.
 {
   'variables' : {
     'pyautolib_sources': [
       'app/chrome_command_ids.h',
       'app/chrome_dll_resource.h',
       'common/automation_constants.h',
       'common/pref_names.cc',
@@ skipping 2755 matching lines @@
         'browser/extensions/api/proxy/proxy_apitest.cc',
         'browser/extensions/api/push_messaging/push_messaging_apitest.cc',
         'browser/extensions/api/record/record_api_test.cc',
         'browser/extensions/api/runtime/runtime_apitest.cc',
         'browser/extensions/api/serial/serial_apitest.cc',
         'browser/extensions/api/socket/socket_apitest.cc',
         'browser/extensions/api/system_info_cpu/system_info_cpu_apitest.cc',
         'browser/extensions/api/tabs/tabs_test.cc',
         'browser/extensions/api/terminal/terminal_private_apitest.cc',
         'browser/extensions/api/test/apitest_apitest.cc',
+        'browser/extensions/api/usb/usb_apitest.cc',
         'browser/extensions/api/web_navigation/web_navigation_apitest.cc',
         'browser/extensions/api/web_request/web_request_apitest.cc',
         'browser/extensions/api/web_socket_proxy_private/web_socket_proxy_private_apitest.cc',
         'browser/extensions/api/webstore_private/webstore_private_apitest.cc',
         'browser/extensions/app_background_page_apitest.cc',
         'browser/extensions/app_notification_browsertest.cc',
         'browser/extensions/app_process_apitest.cc',
         'browser/extensions/autoupdate_interceptor.cc',
         'browser/extensions/autoupdate_interceptor.h',
         'browser/extensions/background_page_apitest.cc',
@@ skipping 1893 matching lines @@
                 '--result', '<@(_outputs)',
                 '--isolate', 'browser_tests.isolate',
               ],
             },
           ],
         },
       ],
     }],
   ],  # 'conditions'
 }