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

chrome/common/extensions/docs/examples/extensions/plugin_settings/js/chrome_stubs.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 Stubs for Chrome extension APIs that aren't available to
  * regular web pages, to allow tests to run.
  */
 
 chrome = chrome || {};
 chrome.extension = chrome.extension || {};
 chrome.contentSettings = chrome.contentSettings || {};
 
 var _rules = {};
 chrome.contentSettings.plugins = {
   'set': function(details, callback) {
     assertObjectEquals({'id': 'myplugin'}, details.resourceIdentifier);
     var pattern = details.primaryPattern;
     var setting = details.setting;
     if (pattern == '__invalid_pattern') {
-      chrome.extension.lastError = {'message': 'Invalid pattern'};
+      chrome.runtime.lastError = {'message': 'Invalid pattern'};
     } else if (setting == '__invalid_setting') {
       throw Error('Invalid setting');
     } else {
-      chrome.extension.lastError = undefined;
+      chrome.runtime.lastError = undefined;
       _rules[pattern] = setting;
     }
     callback();
   },
 
   'clear': function(details, callback) {
     assertObjectEquals({}, details);
     _rules = {};
     callback();
   }
@@ skipping 23 matching lines @@
 function createSettings(rules) {
   var settings = new pluginSettings.Settings('myplugin');
   if (rules) {
     for (var pattern in rules) {
       settings.set(pattern, rules[pattern], function() {});
     }
   }
   return settings;
 }