Make the externally connectable browser test clobber all of the builtins,

chrome/renderer/resources/extensions/media_galleries_custom_bindings.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.
 
 // Custom binding for the Media Gallery API.
 
 var binding = require('binding').Binding.create('mediaGalleries');
 
 var mediaGalleriesNatives = requireNative('mediaGalleries');
 
 var mediaGalleriesMetadata = {};
 
 binding.registerCustomHook(function(bindingsAPI, extensionId) {
   var apiFunctions = bindingsAPI.apiFunctions;
 
   // getMediaFileSystems uses a custom callback so that it can instantiate and
   // return an array of file system objects.
   apiFunctions.setCustomCallback('getMediaFileSystems',
                                  function(name, request, response) {
     var result = null;
     mediaGalleriesMetadata = {};  // Clear any previous metadata.
     if (response) {
       result = [];
       for (var i = 0; i < response.length; i++) {
         var filesystem = mediaGalleriesNatives.GetMediaFileSystemObject(
             response[i].fsid);
-        result.push(filesystem);
+        $Array.push(result, filesystem);
         var metadata = response[i];
         delete metadata.fsid;
         mediaGalleriesMetadata[filesystem.name] = metadata;
       }
     }
     if (request.callback)
       request.callback(result);
     request.callback = null;
   });
 
   apiFunctions.setHandleRequest('getMediaFileSystemMetadata',
                                 function(filesystem) {
     if (filesystem && filesystem.name &&
         mediaGalleriesMetadata[filesystem.name]) {
       return mediaGalleriesMetadata[filesystem.name];
     }
     return {};
   });
 });
 
 exports.binding = binding.generate();