Upstream Service Worker window test to WPT

third_party/WebKit/LayoutTests/external/wpt/service-workers/service-worker/resources/claim-worker.js

 self.addEventListener('message', function(event) {
-    self.clients.claim()
+    event.waitUntil(self.clients.claim()
       .then(function(result) {
           if (result !== undefined) {
               event.data.port.postMessage(
                   'FAIL: claim() should be resolved with undefined');
               return;
           }
           event.data.port.postMessage('PASS');
         })
       .catch(function(error) {
           event.data.port.postMessage('FAIL: exception: ' + error.name);
-        });
+        }));
   });
 
 self.addEventListener('fetch', function(event) {
     event.respondWith(new Response('Intercepted!'));
 });