chromium/content/test/data/accessibility/html/button-alt-changed.html

<!--
@BLINK-ALLOW:name=*
@WAIT-FOR:Done
-->
<!DOCTYPE html>
<html>
<body>
  <div tabindex="0" id="status" aria-label="Working"></div>
  <button>
    <img alt="Before"></img>
  </button>

<script>
setTimeout(function() {
  document.querySelector('img').setAttribute("alt", "After");
  setTimeout(() => {
    document.getElementById('status').setAttribute('aria-label', 'Done');
  }, 0);
}, 1000);
</script>
</body>
</html>