css/css-backgrounds/background-image-cors-no-reload.html

<!doctype html>
<meta charset="utf-8">
<link rel="author" title="Emilio Cobos &Aacute;lvarez" href="mailto:emilio@crisal.io">
<link rel="author" title="Mozilla" href="https://mozilla.org">
<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1832528">
<link rel="help" href="https://drafts.csswg.org/css-backgrounds/">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
:root {
  --icon: url("/images/green.png?variable-cors-no-reload");
}
.item::before,
.item::after {
  display: block;
  content: "";
  height: 1.25rem;
  width: 1.25rem;
  transform: rotate(180deg);
  background: var(--icon) 50%/2rem 2rem;
}
.item::after {
  background: blue;
  mask: var(--icon);
}
.item.toggled::after,
.item.toggled::before {
  color: blue;
}
</style>
<div class="item"></div>
<script>
let t = async_test("CORS image from variable doesn't cause re-downloads");

function getEntries() {
  let url = new URL("/images/green.png?variable-cors-no-reload", location.href).href;
  return performance.getEntriesByName(url);
}

onload = t.step_func(function() {
  let entries = getEntries();
  assert_equals(entries.length, 2, "should be loaded (twice, once with anon cors mode once without)");
  document.querySelector(".item").classList.toggle("toggled");
  // Assume that at least some of the time the load would complete under a second.
  t.step_timeout(t.step_func_done(function() {
    let entries_after = getEntries();
    assert_equals(entries_after.length, entries.length, "Shouldn't have caused re-downloads");
  }), 1000);
});
</script>