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

chrome/renderer/resources/extensions/extension_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 extension API.
 
 var binding = require('binding').Binding.create('extension');
 
 var extensionNatives = requireNative('extension');
 var GetExtensionViews = extensionNatives.GetExtensionViews;
@@ skipping 62 matching lines @@
     'Port',
     // Functions
     'connect', 'sendMessage', 'connectNative', 'sendNativeMessage',
     // Events
     'onConnect', 'onConnectExternal', 'onMessage', 'onMessageExternal'
   ];
   $Array.forEach(mayNeedAlias, function(alias) {
     // Checking existence isn't enough since some functions are disabled via
     // getters that throw exceptions. Assume that any getter is such a function.
     if (chrome.runtime &&
-        chrome.runtime.hasOwnProperty(alias) &&
+        $Object.hasOwnProperty(chrome.runtime, alias) &&
         chrome.runtime.__lookupGetter__(alias) === undefined) {
       extension[alias] = chrome.runtime[alias];
     }
   });
 
   apiFunctions.setUpdateArgumentsPreValidate('sendRequest',
       $Function.bind(miscBindings.sendMessageUpdateArguments,
                       null, 'sendRequest'));
 
   apiFunctions.setHandleRequest('sendRequest',
@@ skipping 11 matching lines @@
     };
     if (contextType == 'BLESSED_EXTENSION') {
       extension.onRequestExternal.addListener = function() {
         throw new Error(sendRequestIsDisabled);
       };
     }
   }
 });
 
 exports.binding = binding.generate();