BrowserTest for delivering push message to service worker.

chrome/test/data/push_messaging/service_worker.js

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Empty service worker script.
+this.onmessage = function(event) {
+  console.log(event);
+  console.log(event.data);
+  sendDataToClients('Message from service worker.');
+};
 
-// TODO(mvanouwerkerk): Add test coverage for push event delivery.
+this.onpush = function(event) {
+  console.log(event);
+  console.log(event.data);
+  sendDataToClients(event.data);
+};
+
+function sendDataToClients(data) {
+  this.clients.getAll().then(function(clients) {
+    clients.forEach(function(client) {
+      client.postMessage(data);
+    });
+  }, function(error) {
+    console.log(error);
+  });
+}