[extension SW] Support lazy events from extension service workers.

chrome/test/data/extensions/api_test/service_worker/events_to_stopped_worker/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 readyPromise = new Promise(function(resolve, reject) {
+  navigator.serviceWorker.register('sw.js').then(function() {
+    return navigator.serviceWorker.ready;
+  }).then(function(registration) {
+    resolve('ready');
+  }).catch(function(err) {
+    reject(err);
+  });
+});
+
+window.runServiceWorker = function() {
+  readyPromise.then(function(message) {
+    window.domAutomationController.send(message);
+  }).catch(function(err) {
+    window.domAutomationController.send('FAILURE');
+  });
+};
+
+window.createTabThenUpdate = function() {
+  navigator.serviceWorker.onmessage = function(e) {
+    if (e.data == 'chrome.tabs.onUpdated callback') {

[Devlin, 2017/06/20 20:31:19]

nit: maybe just send e.data in call cases?  If it's not the expected string,
we'll fail in the C++, so no reason to call "failure" explicitly (and the e.data
value might have something useful?)

[lazyboy, 2017/06/22 02:46:56]

I was more interested in hinting about e.data's value so it's easy to
codesearch.
Hinted that in comment, hopefully that's fine.
Done.

+      window.domAutomationController.send(e.data);
+    } else {
+      window.domAutomationController.send('FAILURE');
+    }
+  };
+  var url = chrome.extension.getURL('on_updated.html');
+  chrome.tabs.create({url: url});
+};