Method preconnect

src/custom-element.js:907–922

* Called to instruct the element to preconnect to hosts it uses during * layout. * @param {boolean} onLayout Whether this was called after a layout. * TODO(#31915): remove once R1 migration is complete.

(onLayout)

     * TODO(#31915): remove once R1 migration is complete.
     */
    preconnect(onLayout) {
      devAssert(this.isUpgraded());
      if (onLayout) {
        this.impl_.preconnectCallback(onLayout);
      } else {
        // If we do early preconnects we delay them a bit. This is kind of
        // an unfortunate trade off, but it seems faster, because the DOM
        // operations themselves are not free and might delay
        startupChunk(this.getAmpDoc(), () => {
          if (!this.ownerDocument || !this.ownerDocument.defaultView) {
            return;
          }
          this.impl_.preconnectCallback(onLayout);
        });
      }
    }

    /**
     * See `BaseElement.R1()`.