<!doctype html>
<html class="test-wait">
<link rel="help" href="https://crbug.com/1077501">
<style>
  @keyframes test {
    from { -webkit-writing-mode: var(--x) }
    to { -webkit-writing-mode: var(--y) }
  }
  div {
    animation: test 1s;
  }
</style>
<div id=div></div>
<script>
window.onload = () => {
  div.offsetTop;
  document.documentElement.classList.remove('test-wait');
};
</script>
</html>