Method getSizer_

src/custom-element.js:981–992

* @return {?Element} * @private

()

     * @private
     */
    getSizer_() {
      if (
        this.sizerElement === undefined &&
        (this.layout_ === Layout_Enum.RESPONSIVE ||
          this.layout_ === Layout_Enum.INTRINSIC)
      ) {
        // Expect sizer to exist, just not yet discovered.
        this.sizerElement = this.querySelector('i-amphtml-sizer');
        this.sizerElement?.setAttribute('slot', 'i-amphtml-svc');
      }
      return this.sizerElement || null;
    }

    /**
     * @param {Element} sizer