Resolve the promise in the service worker event loop

Author: yoshisatoyanagisawa

docs/index.bs

@@ -1630,7 +1630,9 @@ spec: storage; urlPrefix: https://storage.spec.whatwg.org/
                 1. Append |rule| to |allRules|.
 
             1. Set |serviceWorker|'s [=service worker/list of router rules=] to |allRules|.
-            1. Resolve |promise| with undefined.
+            1. Let |serviceWorkerEventLoop| be the [=current global object=]'s [=event loop=].
+            1. [=Queue a task=] to run the following steps on |serviceWorkerEventLoop| using the [=DOM manipulation task source=]:
+                1. Resolve |promise| with undefined.
         1. Return |promise|.
     </section>
   </section>