protected function handle_widget_addition( $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 ) ) );
        $added_widget_ids   = array_diff( $all_new_widget_ids, $all_old_widget_ids );