Add utilities to parse WebUSB device descriptors.

device/usb/usb.gyp

 # Copyright 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.
 
 {
   'variables': {
     'chromium_code': 1,
   },
   'targets': [
     {
@@ skipping 22 matching lines @@
         'usb_device_handle_impl.h',
         'usb_device_handle.h',
         'usb_error.cc',
         'usb_error.h',
         'usb_ids.cc',
         'usb_ids.h',
         'usb_service.cc',
         'usb_service.h',
         'usb_service_impl.cc',
         'usb_service_impl.h',
+        'webusb_descriptors.cc',
+        'webusb_descriptors.h',
       ],
       'actions': [
         {
           'action_name': 'generate_usb_ids',
           'variables': {
             'usb_ids_path%': '../../third_party/usb_ids/usb.ids',
             'usb_ids_py_path': 'tools/usb_ids.py',
           },
           'inputs': [
             '<(usb_ids_path)',
@@ skipping 38 matching lines @@
         'mock_usb_device.cc',
         'mock_usb_device.h',
         'mock_usb_device_handle.cc',
         'mock_usb_device_handle.h',
         'mock_usb_service.cc',
         'mock_usb_service.h',
       ],
     },
   ],
 }