Use promises in notifications tests and enable controlling the page.

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 48 matching lines @@
             messageChannel.port1.addEventListener('message', function(event) {
                 if (event.data == 'ready')
                     resolve({ registration: registration, port: messageChannel.port1 });
             });
 
             registration.active.postMessage(messageChannel.port2, [messageChannel.port2]);
             messageChannel.port1.start();
         });
     });
 }
+
+// Sends a message with |data| over |port|. Returns a promise that either rejects when a bad
+// response message is received, or otherwise resolves with the response data.
+function sendCommand(port, data)
+{
+    return new Promise((resolve, reject) => {
+        port.postMessage(data);
+        port.addEventListener('message', function listener(event) {
+            port.removeEventListener('message', listener);
+            if (typeof event.data != 'object' || !event.data.command) {
+                reject('Invalid message from the Service Worker.');

[Peter Beverloo, 2016/04/21 17:20:56]

nit: Promises should be rejected with errors.

new Error('Invalid message from the Service Worker.')

(Mentally map a rejection handler to the contents of the "catch" in a try {}
catch {}.)

[Michael van Ouwerkerk, 2016/04/22 09:44:22]

Done.

+            } else {
+                resolve(event.data);
+            }
+        });
+    });
+}
+
+// Simulates a click on the notification whose title equals |title|. The |actionIndex| specifies
+// which action button to activate, where -1 means the notification itself is clicked, not an action
+// button.
+function simulateNotificationClick(title, actionIndex, port)
+{
+    return new Promise((resolve, reject) => {
+        testRunner.simulateWebNotificationClick(title, actionIndex);
+        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);
+            }
+        });
+    });
+}