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

chrome/test/data/extensions/api_test/service_worker/events/sw.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 expectedEventData;
+var capturedEventData;
+
+function expect(data) {
+  expectedEventData = data;
+  capturedEventData = [];
+}
+
+var messagePort = null;
+function sendMessage(msg) { messagePort.postMessage(msg); }
+
+function checkExpectations() {
+  if (capturedEventData.length < expectedEventData.length) {
+    return;
+  }
+
+  var passed = JSON.stringify(expectedEventData) ==
+      JSON.stringify(capturedEventData);
+  if (passed) {
+    sendMessage('chrome.tabs.onUpdated callback');
+  } else {
+    sendMessage('FAILURE');
+  }
+}
+
+self.onmessage = function(e) {
+  var data = e.data;
+  messagePort = e.ports[0];
+  if (data == 'addOnUpdatedListener') {
+    addOnUpdatedListener();
+    e.ports[0].postMessage('listener-added');
+  }
+};
+
+function addOnUpdatedListener() {
+  chrome.tabs.onUpdated.addListener(function(tabId, info, tab) {
+    console.log('onUpdated, tabId: ' + tabId + ', info: ' +
+        JSON.stringify(info) + ', tab: ' + JSON.stringify(tab));
+    capturedEventData.push(info);
+    checkExpectations();
+  });
+
+  var url = chrome.extension.getURL('on_updated.html');
+  expect([
+    {status: 'loading', 'url': url},
+    {status: 'complete'},
+    {title: 'foo'},
+    {title: 'bar'}
+  ]);
+};