aura: Use PlatformWindow from WindowTreeHost.

ash/ash.gyp

 # Copyright (c) 2012 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,
     'grit_out_dir': '<(SHARED_INTERMEDIATE_DIR)/chrome',
     # These files lists are shared with the GN build.
     'ash_sources': [
@@ skipping 1013 matching lines @@
         'ash_resources.gyp:ash_resources',
       ],
       'sources': [
         '<@(ash_test_support_sources)',
       ],
       'conditions': [
         ['OS=="win"', {
           'dependencies': [
             '../ipc/ipc.gyp:ipc',
             '../ui/metro_viewer/metro_viewer.gyp:metro_viewer_messages',
+            '../ui/platform_window/win/win_window.gyp:win_window',
             '../win8/win8.gyp:metro_viewer',
             '../win8/win8.gyp:test_support_win8',
             '../win8/win8_tests.gyp:test_registrar',
           ],
           'sources': [
             'test/test_metro_viewer_process_host.cc',
             'test/test_metro_viewer_process_host.h',
           ],
         }],
       ],
@@ skipping 201 matching lines @@
       'conditions': [
         ['chromeos==1', {
           'dependencies': [
             '../ui/display/display.gyp:display',
           ],
         }],
       ],
     },
   ],
 }