chromium/third_party/blink/web_tests/external/wpt/html/browsers/browsing-the-web/navigating-across-documents/replace-before-load/form-submit-popup.html

<!DOCTYPE html>
<meta charset="utf-8">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="resources/helpers.js"></script>

<form target="the-window">
  <input type="hidden" name="pushed">
</form>

<script>
"use strict";
promise_test(async t => {
  const form = document.querySelector("form");
  const wEndingURL = absoluteURL("resources/slow-message-source-with-history-and-location.html?pushed=");
  form.action = wEndingURL;

  const wStartingCode = `
    window.onload = () => { window.onloadFired = true; };
    opener.postMessage({ historyLength: history.length, locationHref: location.href }, "*");
    opener.document.querySelector("form").submit();
  `;

  const wStartingURL = codeInjectorURL(wStartingCode);
  const w = window.open(wStartingURL, "the-window");
  t.add_cleanup(() => w.close());

  const wBeforeLoadedMessage = await waitForMessage();
  assert_equals(wBeforeLoadedMessage.historyLength, 1, "window's starting history.length");
  assert_equals(wBeforeLoadedMessage.locationHref, wStartingURL, "window's starting location.href");
  assert_equals(w.onloadFired, undefined, "window's onload not fired yet");

  const wAfterFormSubmitMessage = await waitForMessage();
  assert_equals(wAfterFormSubmitMessage.historyLength, 2, "window's after-submit history.length");
  assert_equals(wAfterFormSubmitMessage.locationHref, wEndingURL, "window's after-submit location.href");
}, "No replace before load, triggered by formElement.submit() in the opener window, after the opener has loaded");
</script>