Add a function to layout.h for getting ScaleFactor of the native view.

ui/ui.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,
   },
   'includes': [
     'ui_resources.gypi',
@@ skipping 201 matching lines @@
         'base/l10n/l10n_util.cc',
         'base/l10n/l10n_util.h',
         'base/l10n/l10n_util_collator.h',
         'base/l10n/l10n_util_mac.h',
         'base/l10n/l10n_util_mac.mm',
         'base/l10n/l10n_util_posix.cc',
         'base/l10n/l10n_util_win.cc',
         'base/l10n/l10n_util_win.h',
         'base/layout.cc',
         'base/layout.h',
+        'base/layout_mac.mm',
         'base/models/button_menu_item_model.cc',
         'base/models/button_menu_item_model.h',
         'base/models/combobox_model.h',
         'base/models/list_model.h',
         'base/models/list_model_observer.h',
         'base/models/menu_model.cc',
         'base/models/menu_model.h',
         'base/models/menu_model_delegate.h',
         'base/models/simple_menu_model.cc',
         'base/models/simple_menu_model.h',
@@ skipping 526 matching lines @@
                 'shutil.copyfile(\'<(ui_copy_target)\', \'<(ui_copy_dest)\'); ' \
                 'os.chmod(\'<(ui_copy_dest)\', 0700)'
               ]
             }
           ],
         },
       ],
     }],
   ],
 }