Tests that notification resource requests are handled by onfetch.

third_party/WebKit/LayoutTests/http/tests/notifications/resources/test-helpers.js

 // Supports test-runner control messages being send over |messagePort|, which enable
 // workers to have limited access to TestRunner methods.
 function supportTestRunnerMessagesOnPort(messagePort)
 {
     if (!window.testRunner)
         return;
 
     messagePort.addEventListener('message', function(message) {
         if (message.data.type == 'simulateWebNotificationClick')
             testRunner.simulateWebNotificationClick(message.data.title, -1 /* action_index */);
@@ skipping 83 matching lines @@
         port.addEventListener('message', function listener(event) {
             port.removeEventListener('message', listener);
             if (typeof event.data != 'object' || event.data.command != 'click') {
                 reject('Invalid message from the Service Worker.');
             } else {
                 resolve(event.data);
             }
         });
     });
 }
+
+function listenOnce(target, type)

[Peter Beverloo, 2016/04/21 17:27:00]

++docs

[Michael van Ouwerkerk, 2016/04/22 13:24:09]

Done.

+{
+    return new Promise((resolve, reject) => {
+        target.addEventListener(type, function listener(event) {
+            target.removeEventListener(type, listener);
+            resolve(event);
+        });
+    });
+}