ServiceWorker: Wait for the completion of async tasks on ExtendableMessageEvent

third_party/WebKit/LayoutTests/http/tests/serviceworker/resources/clients-matchall-worker.js

 self.onmessage = function(e) {
   var port = e.data.port;
   var options = e.data.options;
 
-  self.clients.matchAll(options).then(function(clients) {
+  e.waitUntil(self.clients.matchAll(options).then(function(clients) {
       var message = [];
       clients.forEach(function(client) {
           message.push([client.visibilityState,
                         client.focused,
                         client.url,
                         client.frameType]);
         });
       port.postMessage(message);
-    });
+    }));
 };