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

LayoutTests/http/tests/serviceworker/client-focus.html

Index: LayoutTests/http/tests/serviceworker/client-focus.html
diff --git a/LayoutTests/http/tests/serviceworker/client-focus.html b/LayoutTests/http/tests/serviceworker/client-focus.html
index 71d677c91c39a9990b2f5459d0017ae0fe2980eb..2ed10fa29806ed371d06d0ff505a6ba2a6664b38 100644
--- a/LayoutTests/http/tests/serviceworker/client-focus.html
+++ b/LayoutTests/http/tests/serviceworker/client-focus.html
@@ -10,10 +10,7 @@ t.step(function() {
     service_worker_unregister_and_register(
         t, 'resources/client-focus.js', scope)
       .then(function(registration) {
-          return wait_for_update(t, registration);
-        })
-      .then(function(sw) {
-          return wait_for_state(t, sw, 'activated');
+          return wait_for_state(t, registration.installing, 'activated');
         })
       .then(function() { return with_iframe(scope); })
       .then(function(frame) {