display-none-iframe-has-no-animation.html

<!DOCTYPE html>
<script src="../resources/testharness.js"></script>
<script src="../resources/testharnessreport.js"></script>
<script type="text/javascript">
  var test = async_test("Tests that children of a display:none iframe do not run animations");

  function go() {
    // Wait a couple of frames for the animation inside the iframe to progress.
    requestAnimationFrame(test.step_func(() => {
      requestAnimationFrame(test.step_func_done(() => {
        var iframe = document.getElementById("iframe");
        iframe.style.display = "block";
        var innerDoc = iframe.contentDocument;
        var target = innerDoc.getElementById('target');

        // If the animation has been running, then we expect "left" to be
        // non-zero.
        assert_equals(parseInt(getComputedStyle(target).left, 10), 0);
      }));
    }));
  };
</script>
<body onload="go()">
  <iframe id="iframe" style="display:none" src="resources/frame_with_animation.html"></iframe>
</body>

chromium/third_party/blink/web_tests/animations/display-none-iframe-has-no-animation.html