Update references to the extension messaging APIs to point to the "runtime"

chrome/common/extensions/docs/examples/extensions/plugin_settings/js/main.js

 // Copyright (c) 2012 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.
 
 /**
  * @fileoverview Main entry point that creates a new plug-in list on document
  * load.
  */
 
 document.addEventListener('DOMContentLoaded', function() {
   chrome.contentSettings.plugins.getResourceIdentifiers(function(r) {
-    if (chrome.extension.lastError) {
+    if (chrome.runtime.lastError) {
       $('error').textContent =
-          'Error: ' + chrome.extension.lastError.message;
+          'Error: ' + chrome.runtime.lastError.message;
       return;
     }
     var pluginList = $('plugin-list');
     pluginSettings.ui.PluginList.decorate(pluginList);
     pluginList.dataModel = new cr.ui.ArrayDataModel(r);
   });
 });