Refactor screen/monitor so that gfx::Screen returns monitor object.

ui/aura/aura.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': [
     {
@@ skipping 55 matching lines @@
         'env.h',
         'env_observer.h',
         'event.cc',
         'event.h',
         'event_filter.h',
         'event_mac.mm',
         'event_mac.h',
         'focus_manager.h',
         'layout_manager.cc',
         'layout_manager.h',
-        'monitor.cc',
-        'monitor.h',
         'monitor_change_observer_x11.cc',
         'monitor_change_observer_x11.h',
         'monitor_manager.cc',
         'monitor_manager.h',
+        'monitor_observer.cc',
+        'monitor_observer.h',
         'root_window_host.h',
         'root_window_host_linux.cc',
         'root_window_host_linux.h',
         'root_window_host_mac.h',
         'root_window_host_mac.mm',
         'root_window_host_win.cc',
         'root_window_host_win.h',
         'root_window_mac.h',
         'root_window_mac.mm',
         'root_window_view_mac.h',
@@ skipping 120 matching lines @@
         # osmesa GL implementation is used on linux.
         ['OS=="linux"', {
           'dependencies': [
             '<(DEPTH)/third_party/mesa/mesa.gyp:osmesa',
           ],
         }],
       ],
     },
   ],
 }