Merge pull request #9330 from youennf/wpt-export-for-webkit-181087

WebKit export of https://bugs.webkit.org/show_bug.cgi?id=181087
diff --git a/service-workers/service-worker/resources/register-closed-window-iframe.html b/service-workers/service-worker/resources/register-closed-window-iframe.html
index ed743ea..117f254 100644
--- a/service-workers/service-worker/resources/register-closed-window-iframe.html
+++ b/service-workers/service-worker/resources/register-closed-window-iframe.html
@@ -1,14 +1,17 @@
 <html>
 <head>
 <script>
-window.addEventListener('message', function(evt) {
+window.addEventListener('message', async function(evt) {
   if (evt.data === 'START') {
     var w = window.open('./');
     var sw = w.navigator.serviceWorker;
     w.close();
     w = null;
-    sw.register('doesntmatter.js');
-    parent.postMessage('OK', '*');
+    try {
+      await sw.register('doesntmatter.js');
+    } finally {
+      parent.postMessage('OK', '*');
+    }
   }
 });
 </script>