protected function handle_widget_removal( $old, $new ) {
        $all_old_widget_ids = array_unique( call_user_func_array( 'array_merge', array_values( $old ) ) );
        $all_new_widget_ids = array_unique( call_user_func_array( 'array_merge', array_values( $new ) ) );
        // @todo In the customizer, moving widgets to other sidebars is problematic because each sidebar is registered as a separate setting; so we need to make sure that all $_POST['customized'] are applied?
        // @todo The widget option is getting updated before the sidebars_widgets are updated, so we need to hook into the option update to try to cache any deletions for future lookup