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

chrome/common/extensions/docs/examples/api/contextMenus/basic/sample.js

 // Copyright (c) 2010 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.
 
 // A generic onclick callback function.
 function genericOnClick(info, tab) {
   console.log("item " + info.menuItemId + " was clicked");
   console.log("info: " + JSON.stringify(info));
   console.log("tab: " + JSON.stringify(tab));
 }
@@ skipping 45 matching lines @@
 var checkbox2 = chrome.contextMenus.create(
   {"title": "Checkbox2", "type": "checkbox", "onclick":checkboxOnClick});
 console.log("checkbox1:" + checkbox1 + " checkbox2:" + checkbox2);
 
 
 // Intentionally create an invalid item, to show off error checking in the
 // create callback.
 console.log("About to try creating an invalid item - an error about " +
             "item 999 should show up");
 chrome.contextMenus.create({"title": "Oops", "parentId":999}, function() {
-  if (chrome.extension.lastError) {
-    console.log("Got expected error: " + chrome.extension.lastError.message);
+  if (chrome.runtime.lastError) {
+    console.log("Got expected error: " + chrome.runtime.lastError.message);
   }
 });