Add PlatformWindow/Event related code for Ozone X11.

ui/ozone/platform/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.
 
 source_set("x11") {
   sources = [
     "client_native_pixmap_factory_x11.cc",
     "client_native_pixmap_factory_x11.h",
     "ozone_platform_x11.cc",
     "ozone_platform_x11.h",
     "x11_surface_factory.cc",
     "x11_surface_factory.h",
   ]
 
   deps = [
     "//base",
     "//skia",
     "//ui/base",
     "//ui/display/types",
     "//ui/display/util",
     "//ui/events",
     "//ui/events/devices",
     "//ui/events/ozone:events_ozone",
     "//ui/events/platform",
+    "//ui/events/platform/x11",
     "//ui/events/x",
     "//ui/gfx",
     "//ui/gfx/geometry",
     "//ui/gfx/x",
     "//ui/ozone:ozone_base",
+    "//ui/platform_window/x11",
   ]
 
   configs += [ "//build/config/linux:x11" ]
 
   public_configs = [ "//third_party/khronos:khronos_headers" ]
 }