[Extensions] More bindings hardening

chrome/renderer/resources/extensions/tag_watcher.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.
 
 function watchForTag(tagName, cb) {
   if (!document.body)
     return;
 
   function findChildTags(queryNode) {
     $Array.forEach(queryNode.querySelectorAll(tagName), function(node) {
@@ skipping 34 matching lines @@
   var useCapture = true;
   window.addEventListener('readystatechange', function listener(event) {
     if (document.readyState == 'loading')
       return;
 
     watchForTag(tagName, cb);
     window.removeEventListener(event.type, listener, useCapture);
   }, useCapture);
 }
 
-exports.addTagWatcher = addTagWatcher;
+exports.$set('addTagWatcher', addTagWatcher);