Method getOverflowElement

src/custom-element.js:2077–2090

* Returns an optional overflow element for this custom element. * @return {?Element}

()

     * @return {?Element}
     */
    getOverflowElement() {
      if (this.overflowElement_ === undefined) {
        this.overflowElement_ = query.childElementByAttr(this, 'overflow');
        if (this.overflowElement_) {
          if (!this.overflowElement_.hasAttribute('tabindex')) {
            this.overflowElement_.setAttribute('tabindex', '0');
          }
          if (!this.overflowElement_.hasAttribute('role')) {
            this.overflowElement_.setAttribute('role', 'button');
          }
        }
      }
      return this.overflowElement_;
    }

    /**
     * Hides or shows the overflow, if available. This function must only