[extension SW]: Support event listener registration and event dispatching.

chrome/test/data/extensions/api_test/service_worker/events/page.js

+// Copyright 2017 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.
+
+var workerPromise = new Promise(function(resolve, reject) {
+  navigator.serviceWorker.register('sw.js').then(function() {
+    return navigator.serviceWorker.ready;
+  }).then(function(registration) {
+    var sw = registration.active;
+    var channel = new MessageChannel();
+    channel.port1.onmessage = function(e) {
+      var data = e.data;
+      console.error('data: ' + data);

[Devlin, 2017/06/01 04:54:49]

probably remove this or replace with chrome.test.log; at least replace with
console.log so it doesn't look like an error.

[lazyboy, 2017/06/01 23:33:29]

Removed.

+      if (data == 'listener-added') {
+        var url = chrome.extension.getURL('on_updated.html');
+        chrome.tabs.create({url: url});
+      } else if (data == 'chrome.tabs.onUpdated callback') {
+        resolve(data);
+      } else {
+        reject(data);
+      }
+    };
+    sw.postMessage('addOnUpdatedListener', [channel.port2]);
+  }).catch(function(err) {
+    reject(err);
+  });
+});
+
+window.runEventTest = function() {
+  workerPromise.then(function(message) {
+    window.domAutomationController.send(message);
+  }).catch(function(err) {
+    window.domAutomationController.send('FAILURE');
+  });
+};