Form submissions opening in a new window don't need special treatment anymore.

third_party/WebKit/LayoutTests/http/tests/navigation/resources/post-with-modifier.php

 <script>
-if (window.opener) {
-    var data = {
-        'method': '<?=$_SERVER['REQUEST_METHOD'] ?>',
-        'formValue': '<?= $_POST['a'] ?>',
-    };
-    window.opener.postMessage(data, '*');
-} else {
-    document.writeln('FAIL');
-    testRunner.notifyDone();
-}
+mainTestWindow = window.open("", "mainTestWindow")
+var data = {
+    'method': '<?=$_SERVER['REQUEST_METHOD'] ?>',
+    'formValue': '<?= $_POST['a'] ?>',
+};
+mainTestWindow.postMessage(data, '*');
 </script>