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

ui/events/platform/x11/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/ui.gni")
 import("//ui/ozone/ozone.gni")
 
 assert(use_x11 || ozone_platform_x11)
 
 component("x11") {
   output_name = "x11_events_platform"
 
   sources = [
     "x11_event_source.cc",
     "x11_event_source.h",
     "x11_hotplug_event_handler.cc",
     "x11_hotplug_event_handler.h",
   ]
 
   defines = [ "EVENTS_IMPLEMENTATION" ]
 
   configs += [ "//build/config/linux:x11" ]
 
   public_deps = [
     "//ui/events",
     "//ui/events:events_base",
     "//ui/events/devices",
+    "//ui/events/devices/x11",
     "//ui/events/platform",
     "//ui/events/x",
     "//ui/gfx/x",
   ]
 
   deps = [
     "//base",
   ]
 
   if (use_glib) {
     sources += [
       "x11_event_source_glib.cc",
       "x11_event_source_glib.h",
     ]
 
     configs += [ "//build/config/linux:glib" ]
   } else {
     sources += [
       "x11_event_source_libevent.cc",
       "x11_event_source_libevent.h",
     ]
   }
 }