  onload = () => {
                requestAnimationFrame(() => { requestAnimationFrame(() => {
                  // First full rendering update is complete.
                  let resize_event_count = 0;
                  iframe.contentWindow.visualViewport.addEventListener("resize", () => {
                    resize_event_count++;
                  });
                  iframe.style.display = "";
                  iframe.clientWidth;
                  requestAnimationFrame(() => {
                    t.ste