Split //ui/events/devices into two targets.

ui/events/x/events_x.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': [
     {
       # GN version: //ui/events/x
       'target_name': 'events_x',
       'type': '<(component)',
       'dependencies': [
         '<(DEPTH)/base/base.gyp:base',
         '<(DEPTH)/skia/skia.gyp:skia',
         '../../events/devices/events_devices.gyp:events_devices',
+        '../../events/devices/x11/events_devices_x11.gyp:events_devices_x11',
         '../../events/events.gyp:events_base',
         '../../gfx/x/gfx_x11.gyp:gfx_x11',
       ],
       'defines': [
         'EVENTS_X_IMPLEMENTATION',
       ],
       'sources': [
         'events_x_export.h',
         'events_x_utils.cc',
         'events_x_utils.h',
       ],
       'conditions': [
         ['use_x11==1', {
           'dependencies': [
             '<(DEPTH)/build/linux/system.gyp:x11',
           ],
         }],
       ],
     },
   ],
 }