HTML: test queueing behavior of window.close()

For whatwg/html#4402.

html/browsers/the-window-object/close-method.window.js

@@ -0,0 +1,39 @@
+function assert_closed_opener(w, closed, opener) {
+  assert_equals(w.closed, closed);
+  assert_equals(w.opener, opener);
+}
+
+async_test(t => {
+  const openee = window.open();
+  assert_closed_opener(openee, false, self);
+  openee.onunload = t.step_func(() => {
+    assert_closed_opener(openee, true, self);
+    t.step_timeout(() => {
+      assert_closed_opener(openee, true, null);
+      t.done();
+    }, 0);
+  });
+  openee.close();
+  assert_closed_opener(openee, true, self);
+}, "window.close() queues a task to discard, but window.closed knows immediately");
+
+async_test(t => {
+  const openee = window.open("", "greatname");
+  assert_closed_opener(openee, false, self);
+  openee.close();
+  assert_closed_opener(openee, true, self);
+  const openee2 = window.open("", "greatname");
+  assert_not_equals(openee, openee2);
+  assert_closed_opener(openee, true, self); // Ensure second window.open() call was synchronous
+  openee2.onunload = t.step_func(() => {
+    assert_closed_opener(openee2, true, self);
+    t.step_timeout(() => {
+      assert_closed_opener(openee, true, null);
+      assert_closed_opener(openee2, true, null);
+      t.done();
+    }, 0);
+  });
+  openee2.close();
+  assert_closed_opener(openee, true, self); // Ensure second close() call was synchronous
+  assert_closed_opener(openee2, true, self);
+}, "window.close() affects name targeting immediately");