ash: Clean up system background layer.

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',
   },
   'includes': [
@@ skipping 333 matching lines @@
         'wm/shadow_controller.h',
         'wm/shadow_types.cc',
         'wm/shadow_types.h',
         'wm/shelf_layout_manager.cc',
         'wm/shelf_layout_manager.h',
         'wm/shelf_types.h',
         'wm/stacking_controller.cc',
         'wm/stacking_controller.h',
         'wm/status_area_layout_manager.cc',
         'wm/status_area_layout_manager.h',
+        'wm/system_background_controller.cc',
+        'wm/system_background_controller.h',
         'wm/system_gesture_event_filter.cc',
         'wm/system_gesture_event_filter.h',
         'wm/system_modal_container_event_filter.cc',
         'wm/system_modal_container_event_filter.h',
         'wm/system_modal_container_event_filter_delegate.h',
         'wm/system_modal_container_layout_manager.cc',
         'wm/system_modal_container_layout_manager.h',
         'wm/toplevel_window_event_handler.cc',
         'wm/toplevel_window_event_handler.h',
         'wm/user_activity_detector.cc',
@@ skipping 330 matching lines @@
             'shell/cocoa/app-Info.plist',
           ],
           'xcode_settings': {
             'INFOPLIST_FILE': 'shell/cocoa/app-Info.plist',
           },
         }],
       ],
     },
   ],
 }