mash: Remove WmRootWindowControllerObserver.

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,
     # These files lists are shared with the GN build.
     'ash_sources': [
       'accelerators/accelerator_commands_aura.cc',
@@ skipping 513 matching lines @@
       'common/wm/workspace/workspace_window_resizer.h',
       'common/wm/workspace_controller.cc',
       'common/wm/workspace_controller.h',
       'common/wm_activation_observer.h',
       'common/wm_display_observer.h',
       'common/wm_layout_manager.h',
       'common/wm_lookup.cc',
       'common/wm_lookup.h',
       'common/wm_root_window_controller.cc',
       'common/wm_root_window_controller.h',
-      'common/wm_root_window_controller_observer.h',
       'common/wm_shell.cc',
       'common/wm_shell.h',
       'common/wm_transient_window_observer.h',
       'common/wm_window.h',
       'common/wm_window_observer.h',
       'common/wm_window_property.h',
       'common/wm_window_tracker.h',
       'debug.cc',
       'debug.h',
       'default_wallpaper_delegate.cc',
@@ skipping 968 matching lines @@
                   '../tools/xdisplaycheck/xdisplaycheck.gyp:xdisplaycheck',
                 ],
               }
             ],
           ],
         },
       ],
     }],
   ],
 }