code: public function init()
      {
          parent::init();
          if ($this->percent !== null) {
              $this->clientOptions['percent'] = $this->percent;
          }
          if (!empty($this->size)) {
              Html::addCssClass($this->options, $this->size);
          }
          Html::addCssClass($this->barOptions, 'bar');
          Html::addCssClass($this->options, 'progress');
      }
docs: Initializes the widget.
  If you override this method, make sure you call the parent implementation first.