chromium/chrome/test/data/delayed_mixed_content.html

<!DOCTYPE html>
<!-- Loads passive mixed content on request. -->
<html>
<body>
<div id="container"></div>
<script>
function load_mixed() {
  var img = document.createElement('img');
  img.src = "http://a.test/image.jpg";
  document.getElementById("container").appendChild(img);
};
</script>
</body>
</html>