void Shell::CreateModalBackground(aura::Window* window) {
  if (!modality_filter_) {
    modality_filter_.reset(new SystemModalContainerEventFilter(this));
    AddPreTargetHandler(modality_filter_.get());
  }
  RootWindowControllerList controllers = GetAllRootWindowControllers();
  for (RootWindowControllerList::iterator iter = controllers.begin();
       iter != controllers.end(); ++iter)
    (*iter)->GetSystemModalLayoutManager(window)->CreateModalBackground();
}

Unknown