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

chrome/renderer/resources/extensions/file_system_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 fileSystem API.
 
 var binding = require('binding').Binding.create('fileSystem');
 
 var fileSystemNatives = requireNative('file_system_natives');
 var GetIsolatedFileSystem = fileSystemNatives.GetIsolatedFileSystem;
@@ skipping 58 matching lines @@
 }
 
 binding.registerCustomHook(function(bindingsAPI) {
   var apiFunctions = bindingsAPI.apiFunctions;
   var fileSystem = bindingsAPI.compiledApi;
 
   function bindFileEntryFunction(functionName) {
     apiFunctions.setUpdateArgumentsPostValidate(
         functionName, function(fileEntry, callback) {
       var fileSystemName = fileEntry.filesystem.name;
-      var relativePath = fileEntry.fullPath.slice(1);
+      var relativePath = $String.slice(fileEntry.fullPath, 1);
       return [fileSystemName, relativePath, callback];
     });
   }
   $Array.forEach(['getDisplayPath', 'getWritableEntry', 'isWritableEntry'],
                   bindFileEntryFunction);
 
   $Array.forEach(['getWritableEntry', 'chooseEntry', 'restoreEntry'],
                   function(functionName) {
     bindFileEntryCallback(functionName, apiFunctions);
   });
 
   apiFunctions.setHandleRequest('retainEntry', function(fileEntry) {
     var id = entryIdManager.getEntryId(fileEntry);
     if (!id)
       return '';
     var fileSystemName = fileEntry.filesystem.name;
-    var relativePath = fileEntry.fullPath.slice(1);
+    var relativePath = $String.slice(fileEntry.fullPath, 1);
 
     sendRequest(this.name, [id, fileSystemName, relativePath],
       this.definition.parameters, {});
     return id;
   });
 
   apiFunctions.setHandleRequest('isRestorable',
       function(id, callback) {
     var savedEntry = entryIdManager.getEntryById(id);
     if (savedEntry) {
@@ skipping 15 matching lines @@
       // Ask the browser process for a new file entry for this id, to be passed
       // to |callback|.
       return [id, true, callback];
     }
   });
 
   // TODO(benwells): Remove these deprecated versions of the functions.
   fileSystem.getWritableFileEntry = function() {
     console.log("chrome.fileSystem.getWritableFileEntry is deprecated");
     console.log("Please use chrome.fileSystem.getWritableEntry instead");
-    fileSystem.getWritableEntry.apply(this, arguments);
+    $Function.apply(fileSystem.getWritableEntry, this, arguments);
   };
 
   fileSystem.isWritableFileEntry = function() {
     console.log("chrome.fileSystem.isWritableFileEntry is deprecated");
     console.log("Please use chrome.fileSystem.isWritableEntry instead");
-    fileSystem.isWritableEntry.apply(this, arguments);
+    $Function.apply(fileSystem.isWritableEntry, this, arguments);
   };
 
   fileSystem.chooseFile = function() {
     console.log("chrome.fileSystem.chooseFile is deprecated");
     console.log("Please use chrome.fileSystem.chooseEntry instead");
-    fileSystem.chooseEntry.apply(this, arguments);
+    $Function.apply(fileSystem.chooseEntry, this, arguments);
   };
 });
 
 exports.bindFileEntryCallback = bindFileEntryCallback;
 exports.binding = binding.generate();