Add a test to cover service worker update codepath when extension is updated

chrome/test/data/extensions/api_test/service_worker/update/v1/background.js

+// Copyright 2015 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 serviceWorkerPromise = 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) {
+      if (e.data == 'Pong from version 1') {
+        resolve(e.data);
+      } else {
+        reject(e.data);  // Fail fast.
+      }
+    };
+    sw.postMessage('ping', [channel.port2]);
+  }).catch(function(err) {
+    reject(err);
+  });
+});
+
+serviceWorkerPromise.then(function(message) {
+  chrome.test.sendMessage(message);
+}).catch(function(err) {
+  chrome.test.sendMessage('FAILURE_V1');
+});