Make aura_demo work on Mac

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 71 matching lines @@
         'env.h',
         'env_observer.h',
         'input_state_lookup.cc',
         'input_state_lookup.h',
         'input_state_lookup_win.cc',
         'input_state_lookup_win.h',
         'layout_manager.cc',
         'layout_manager.h',
         'remote_root_window_host_win.cc',
         'remote_root_window_host_win.h',
+        'root_window_host_mac.mm',
+        'root_window_host_mac.h',
         'root_window_host_ozone.cc',
         'root_window_host_ozone.h',
         'root_window_host_win.cc',
         'root_window_host_win.h',
         'root_window_host_x11.cc',
         'root_window_host_x11.h',
         'root_window_transformer.h',
         'root_window.cc',
         'root_window.h',
         'window.cc',
@@ skipping 176 matching lines @@
         ['OS=="linux" and linux_use_tcmalloc==1', {
           'dependencies': [
            # See http://crbug.com/162998#c4 for why this is needed.
             '../../base/allocator/allocator.gyp:allocator',
           ],
         }],
       ],
     },
   ],
 }