chromium/src/third_party/blink/web_tests/external/wpt/window-segments/post-window-segments-sub-frame.html

<script>
let segments = getWindowSegments();

parent.postMessage({
    length: segments.length,
    x: segments[0].x,
    y: segments[0].y,
    width: segments[0].width,
    height: segments[0].height,
    domain: document.domain,
  }, "*");
</script>