ServiceWorker cleanup: remove wait_for_update() in favor of r.installing in most tests

LayoutTests/http/tests/serviceworker/state.html

Index: LayoutTests/http/tests/serviceworker/state.html
diff --git a/LayoutTests/http/tests/serviceworker/state.html b/LayoutTests/http/tests/serviceworker/state.html
index a94f32034560fe77528ca06bbf6e4d615d9949a3..ddc08d563c6c7fb6de92107a256c784b504b529a 100644
--- a/LayoutTests/http/tests/serviceworker/state.html
+++ b/LayoutTests/http/tests/serviceworker/state.html
@@ -12,9 +12,7 @@
     service_worker_unregister_and_register(
         t, 'resources/empty-worker.js', scope)
       .then(t.step_func(function(registration) {
-          return wait_for_update(t, registration);
-        }))
-      .then(t.step_func(function(sw) {
+          var sw = registration.installing;
           sw.addEventListener('statechange', t.step_func(onStateChange(sw)));
           assert_equals(sw.state, 'installing',
                         'the service worker should be in "installing" state.');