Method initialize_

third_party/subscriptions-project/swg.js:15424–15427

* Appends the iframe to the DOM and updates the post message service. * @private

()

   * @private
   */
  static initialize_() {
    document.body.appendChild(iframe);
    postMessageService = new PostMessageService(iframe.contentWindow);
  }

  /**
   * Sends a message to the iframe and wait for a response.