[Extensions] More bindings hardening

chrome/renderer/resources/extensions/app_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 app API.
 
 var GetAvailability = requireNative('v8_context').GetAvailability;
 if (!GetAvailability('app').is_available) {
-  exports.binding = {};
-  exports.onInstallStateResponse = function(){};
+  exports.$set('binding', {});
+  exports.$set('onInstallStateResponse', function(){});
   return;
 }
 
 var appNatives = requireNative('app');
 var process = requireNative('process');
 var extensionId = process.GetExtensionId();
 var logActivity = requireNative('activityLogger');
 
 function wrapForLogging(fun) {
   if (!extensionId)
@@ skipping 42 matching lines @@
 var nextCallbackId = 1;
 
 app.installState = function getInstallState(callback) {
   var callbackId = nextCallbackId++;
   callbacks[callbackId] = callback;
   appNatives.GetInstallState(callbackId);
 };
 if (extensionId)
   app.installState = wrapForLogging(app.installState);
 
-exports.binding = app;
-exports.onInstallStateResponse = onInstallStateResponse;
+exports.$set('binding', app);
+exports.$set('onInstallStateResponse', onInstallStateResponse);