ServiceWorker: Enable ServiceWorkerRegistration and update layout tests

LayoutTests/http/tests/serviceworker/resources/test-helpers.js

Index: LayoutTests/http/tests/serviceworker/resources/test-helpers.js
diff --git a/LayoutTests/http/tests/serviceworker/resources/test-helpers.js b/LayoutTests/http/tests/serviceworker/resources/test-helpers.js
index 51d8ebbb0a4f05b4233d4301cd7c5dbab359481d..9efff87884b3258ca7c6396b68c3ff108f21dd5a 100644
--- a/LayoutTests/http/tests/serviceworker/resources/test-helpers.js
+++ b/LayoutTests/http/tests/serviceworker/resources/test-helpers.js
@@ -59,6 +59,14 @@ function normalizeURL(url) {
   return new URL(url, document.location).toString().replace(/#.*$/, '');
 }
 
+function wait_for_update(test, registration) {
+    return new Promise(test.step_func(function(resolve, reject) {
+        registration.addEventListener('updatefound', test.step_func(function() {
+            resolve(registration.installing);
+        }));
+    }));
+}
+
 function wait_for_state(test, worker, state) {
     return new Promise(test.step_func(function(resolve, reject) {
         worker.addEventListener('statechange', test.step_func(function() {
@@ -112,6 +120,9 @@ function wait_for_state(test, worker, state) {
 
     var test = async_test(description);
     service_worker_unregister_and_register(test, url, scope)
+      .then(function(registration) {
+          return wait_for_update(test, registration);
+        })
       .then(function(worker) { return fetch_tests_from_worker(worker); })
       .then(function() { return navigator.serviceWorker.unregister(scope); })
       .then(function() { test.done(); })