Fix mistaken use of promise in multiple-register.html

LayoutTests/http/tests/serviceworker/multiple-register.html

Index: LayoutTests/http/tests/serviceworker/multiple-register.html
diff --git a/LayoutTests/http/tests/serviceworker/multiple-register.html b/LayoutTests/http/tests/serviceworker/multiple-register.html
index 33fb716b5a0af50e607ceeef1f23e0614e2427e4..4e6841925a75b8c717aec21922fc2bb737d6b245 100644
--- a/LayoutTests/http/tests/serviceworker/multiple-register.html
+++ b/LayoutTests/http/tests/serviceworker/multiple-register.html
@@ -22,8 +22,8 @@ async_test(function(t) {
                       'register should resolve to the same worker');
         assert_equals(registered_worker.state, 'activated',
                       'the worker should be in state "activated"');
+        service_worker_unregister_and_done(t, scope);
       })
-    .then(service_worker_unregister_and_done(t, scope))
     .catch(unreached_rejection(t));
 }, 'Subsequent registrations resolve to the same worker');
 
@@ -45,8 +45,8 @@ async_test(function(t) {
             assert_equals(worker, workers[0],
                           'register should resolve to the same worker');
         });
+        service_worker_unregister_and_done(t, scope);
       })
-    .then(service_worker_unregister_and_done(t, scope))
     .catch(unreached_rejection(t));
 }, 'Concurrent registrations resolve to the same worker');
 </script>