Add ServiceWorker InstallPhaseEvent.waitUntil() layout test.

LayoutTests/http/tests/serviceworker/service-worker-gc.html

Index: LayoutTests/http/tests/serviceworker/service-worker-gc.html
diff --git a/LayoutTests/http/tests/serviceworker/service-worker-gc.html b/LayoutTests/http/tests/serviceworker/service-worker-gc.html
index 633a380ecf81c85c96e9f851b82d942f20c097b2..d801f20f7eaed7ac99ca8a5adda29b5c2e5b8736 100644
--- a/LayoutTests/http/tests/serviceworker/service-worker-gc.html
+++ b/LayoutTests/http/tests/serviceworker/service-worker-gc.html
@@ -42,7 +42,7 @@ function onRegister(sw) {
 function onStateChange(event) {
     assertServiceWorkerIsNotCollected();
 
-    if (event.target.state != 'active')
+    if (event.target.state != 'activated')
         return;
     navigator.serviceWorker.unregister(scope).then(onUnregister);
 }