Test that javascript: URL navigation does not fire beforeunload

The current spec fires beforeunload, but the rewrite in whatwg/html#6315 does not.

html/browsers/browsing-the-web/navigating-across-documents/javascript-url-no-beforeunload.window.js

@@ -0,0 +1,80 @@
+// META: script=../resources/helpers.js
+
+for (const stringCompletion of [false, true]) {
+  const testNameSuffix = stringCompletion ? ": string completion" : ": undefined completion";
+
+  testNoBeforeunload(
+    { testRunnerWindow: "top", stringCompletion },
+    async (t, urlToSet) => {
+      const iframe = await addIframe();
+      iframe.contentWindow.location.href = urlToSet;
+
+      return iframe.contentWindow;
+    },
+    `Navigating an iframe via location.href to a javascript: URL must not fire beforeunload${testNameSuffix}`
+  );
+
+  testNoBeforeunload(
+    { testRunnerWindow: "top", stringCompletion },
+    async (t, urlToSet) => {
+      const iframe = await addIframe();
+      iframe.src = urlToSet;
+
+      return iframe.contentWindow;
+    },
+    `Navigating an iframe via src="" to a javascript: URL after insertion must not fire beforeunload${testNameSuffix}`
+  );
+
+  testNoBeforeunload(
+    { testRunnerWindow: "opener", stringCompletion },
+    async (t, urlToSet) => {
+      const w = await openWindow("/common/blank.html", t);
+      w.location.href = urlToSet;
+
+      return w;
+    },
+    `Navigating an opened window via location.href to a javascript: URL must not fire beforeunload${testNameSuffix}`
+  );
+
+
+  testNoBeforeunload(
+    { testRunnerWindow: "opener", stringCompletion },
+    async (t, urlToSet) => {
+      const w = await openWindow("../resources/has-iframe.html", t);
+      w.frames[0].onbeforeunload = t.unreached_func("beforeunload must not fire on the iframe");
+      w.location.href = urlToSet;
+
+      return w;
+    },
+    `Navigating an opened window with an iframe via location.href to a javascript: URL must not fire beforeunload on the iframe${testNameSuffix}`
+  );
+}
+
+function testNoBeforeunload({ testRunnerWindow, stringCompletion }, setupAndNavigateFunc, description) {
+  promise_test(async t => {
+    t.add_cleanup(() => {
+      delete window.resolveTestPromise;
+    });
+
+    const ranPromise = new Promise(resolve => {
+      window.resolveTestPromise = resolve;
+    });
+
+    const urlToSet = makeURL({ testRunnerWindow, stringCompletion });
+    const w = await setupAndNavigateFunc(t, urlToSet);
+    w.onbeforeunload = t.unreached_func("beforeunload must not fire");
+
+    await ranPromise;
+    if (stringCompletion) {
+      await waitForMessage(w);
+    }
+  }, description);
+}
+
+function makeURL({ testRunnerWindow, stringCompletion }) {
+  const completion = stringCompletion ?
+    `"a string<script>window.${testRunnerWindow}.postMessage('ready', '*');</script>";` :
+    `undefined;`;
+
+  return `javascript:window.${testRunnerWindow}.resolveTestPromise();${completion};`;
+}