<!DOCTYPE HTML>
<iframe src="http://example.org/tests/dom/html/test/bug1315146-iframe.html"></iframe>
<input value="test">
<script>
document.domain = "example.org";
onload = function() {
  let iframe = document.querySelector("iframe");
  let input = document.querySelector("input");
  input.selectionStart = input.selectionEnd = 2;
  document.body.style.overflow = "scroll";
  iframe.contentDocument.body.offsetWidth;
  opener.postMessage({start: input.selectionStart,
                      end: input.selectionEnd}, "*");
}
</script>
