chromium/src/third_party/blink/web_tests/http/tests/images/png-animated-partial-load.html

<img style="background: green" >
<script>
if (window.testRunner)
  testRunner.waitUntilDone();

function loadAndStall()
{
  return "http://127.0.0.1:8000/resources/load-and-stall.php";
}

function apngImage()
{
  return "?name=../../../images/resources/count-down-color-test.png&mimeType=image%2Fapng";
}

function testDone()
{
  window.testRunner && testRunner.notifyDone();
}

function runTest()
{
  document.querySelector("img").src = loadAndStall() + apngImage() + "&stallAt=9252&stallFor=60";
  setTimeout(testDone, 1500);
}

window.onload = function() {
  setTimeout(runTest, 0);
}
</script>