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

ui/events/devices/x11/BUILD.gn

 # 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.
 
 component("x11") {
   output_name = "events_devices_x11"
 
   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",
   ]
 
   configs += [ "//build/config/linux:x11" ]
 
   defines = [ "EVENTS_DEVICES_X11_IMPLEMENTATION" ]
 
   deps = [
     "//base",
     "//base/third_party/dynamic_annotations",
     "//skia",
     "//ui/display",
     "//ui/events:events_base",
     "//ui/events/devices",
     "//ui/events/keycodes:x11",
     "//ui/gfx",
     "//ui/gfx/geometry",
     "//ui/gfx/x",
   ]
 }