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

chrome/renderer/resources/extensions/experimental.offscreenTabs_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 experimental offscreenTabs API.
 
 var binding = require('binding').Binding.create('experimental.offscreenTabs');
 
 binding.registerCustomHook(
     'experimental.offscreenTabs', function(api) {
@@ skipping 27 matching lines @@
       button: e.button,
     };
     maybeCopy(e, 'wheelDeltaX', result);
     maybeCopy(e, 'wheelDeltaY', result);
     return result;
   };
 
   // We are making a copy of |arr|, but applying |func| to index 1.
   function validate(arr, func) {
     var newArr = [];
-    for (var i = 0; i < arr.length; i++)
-      newArr.push(i == 1 && typeof(arr) == 'object' ? func(arr[i]) : arr[i]);
+    for (var i = 0; i < arr.length; i++) {
+      $Array.push(newArr,
+                  i == 1 && typeof(arr) == 'object' ? func(arr[i]) : arr[i]);
+    }
     return newArr;
   }
 
   apiFunctions.setUpdateArgumentsPreValidate(
       'sendKeyboardEvent',
       function() { return validate(arguments, keyboardEventFilter); });
   apiFunctions.setUpdateArgumentsPreValidate(
       'sendMouseEvent',
       function() { return validate(arguments, mouseEventFilter); });
 });
 
 exports.binding = binding.generate();