transform-usecounter-3d-iframe.html

<!DOCTYPE HTML>
<style>
#transform { width: 50px; height: 50px; background: blue; }
</style>

<div style="transform-style: preserve-3d">
  <div id="transform" style="transform: translateZ(20px)"></div>
</div>

<script>
window.addEventListener("message", function(event) {
  window.parent.postMessage(internals.isUseCounted(document, event.data), "*");
});
</script>

chromium/third_party/blink/web_tests/http/tests/misc/resources/transform-usecounter-3d-iframe.html