Added a command line switch to disable xinput2, enabled xinput2 by default

ui/events/devices/x11/events_devices_x11.gyp

 # Copyright 2016 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 15 matching lines @@
         'EVENTS_DEVICES_X11_IMPLEMENTATION',
       ],
       'sources': [
         'device_data_manager_x11.cc',
         'device_data_manager_x11.h',
         'device_list_cache_x11.cc',
         'device_list_cache_x11.h',
         'events_devices_x11_export.h',
         'touch_factory_x11.cc',
         'touch_factory_x11.h',
+        'ui_events_devices_x11_switches.cc',
+        'ui_events_devices_x11_switches.h',
       ],
     },
   ],
 }