chromium/third_party/blink/web_tests/http/tests/security/mixedContent/insecure-formSubmission-in-invisible-DOM.html

<html>
<body>
<script>
if (window.testRunner) {
  testRunner.waitUntilDone();
  testRunner.dumpAsText();
  testRunner.setPopupBlockingEnabled(false);
}

window.addEventListener("message", function(e) {
  if (window.testRunner)
    testRunner.notifyDone();
}, false);
</script>

<p>This test opens a window that has an invisible DOM created using "createHTMLDocument" with a form pointing to an insecure location from a secure origin (crbug/398066).</p>

<script>
window.open("https://127.0.0.1:8443/security/mixedContent/resources/frame-with-invisible-DOM-with-insecure-form.html");
</script>
</body>
</html>