Merge three implementations for getting the topmost x11 window at a point

ui/views/views.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,
   },
   'targets': [
     {
       'target_name': 'views',
@@ skipping 336 matching lines @@
         'widget/desktop_aura/desktop_screen_win.cc',
         'widget/desktop_aura/desktop_screen_win.h',
         'widget/desktop_aura/desktop_screen_x11.cc',
         'widget/desktop_aura/desktop_screen_x11.h',
         'widget/desktop_aura/x11_desktop_handler.cc',
         'widget/desktop_aura/x11_desktop_handler.h',
         'widget/desktop_aura/x11_desktop_window_move_client.cc',
         'widget/desktop_aura/x11_desktop_window_move_client.h',
         'widget/desktop_aura/x11_scoped_capture.cc',
         'widget/desktop_aura/x11_scoped_capture.h',
+        'widget/desktop_aura/x11_topmost_window_finder.cc',
+        'widget/desktop_aura/x11_topmost_window_finder.h',
         'widget/desktop_aura/x11_whole_screen_move_loop.cc',
         'widget/desktop_aura/x11_whole_screen_move_loop.h',
         'widget/desktop_aura/x11_whole_screen_move_loop_delegate.h',
         'widget/desktop_aura/x11_window_event_filter.cc',
         'widget/desktop_aura/x11_window_event_filter.h',
         'widget/drop_helper.cc',
         'widget/drop_helper.h',
         'widget/root_view.cc',
         'widget/root_view.h',
         'widget/monitor_win.cc',
@@ skipping 322 matching lines @@
         }],
         ['use_ozone==1', {
           'sources!': [
             'corewm/capture_controller_unittest.cc',
           ],
         }],
       ],
     },  # target_name: views_unittests
   ],
 }