chromium/third_party/blink/web_tests/http/tests/linkHeader/link-dnsprefetch-in-image.html

<!DOCTYPE html>
<script>
    if (window.testRunner) {
        testRunner.dumpAsText();
        testRunner.waitUntilDone();
    }
    if (window.internals) {
        internals.settings.setLogDnsPrefetchAndPreconnect(true);
    }
    document.write("<img src='resources/link-dnsprefetch-image.php' onload='if (window.testRunner)testRunner.notifyDone()'>");
</script>
This test checks if a Link header inside an image triggered a dns prefetch.