[Extensions] Improve app custom bindings

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 appNatives = requireNative('app');
 var process = requireNative('process');
 var extensionId = process.GetExtensionId();
 var logActivity = requireNative('activityLogger');
@@ skipping 17 matching lines @@
   getDetails: wrapForLogging(appNatives.GetDetails),
   runningState: wrapForLogging(appNatives.GetRunningState)
 };
 
 // Tricky; "getIsInstalled" is actually exposed as the getter "isInstalled",
 // but we don't have a way to express this in the schema JSON (nor is it
 // worth it for this one special case).
 //
 // So, define it manually, and let the getIsInstalled function act as its
 // documentation.
-app.__defineGetter__('isInstalled', wrapForLogging(appNatives.GetIsInstalled));
+$Object.defineProperty(

[Devlin, 2017/05/04 18:58:50]

all these changes are just to guard against untrusted code.

+    app, 'isInstalled',
+    {
+      __proto__: null,
+      configurable: true,
+      enumerable: true,
+      writable: true,
+      get: wrapForLogging(appNatives.GetIsInstalled),
+    });
 
 // Called by app_bindings.cc.
 function onInstallStateResponse(state, callbackId) {
   var callback = callbacks[callbackId];
   delete callbacks[callbackId];
-  if (typeof(callback) == 'function') {
+  if (typeof callback == 'function') {
     try {
       callback(state);
     } catch (e) {
       console.error('Exception in chrome.app.installState response handler: ' +
                     e.stack);
     }
   }
 }
 
 // TODO(kalman): move this stuff to its own custom bindings.
-var callbacks = {};
+var callbacks = { __proto__: null };
 var nextCallbackId = 1;
 
-app.installState = function getInstallState(callback) {
+function getInstallState(callback) {
   var callbackId = nextCallbackId++;
   callbacks[callbackId] = callback;
   appNatives.GetInstallState(callbackId);
-};
-if (extensionId)
-  app.installState = wrapForLogging(app.installState);
+}
+
+$Object.defineProperty(
+    app, 'installState',
+    {
+      __proto__: null,
+      configurable: true,
+      enumerable: true,
+      writable: true,
+      get: wrapForLogging(getInstallState),
+    });
 
 exports.$set('binding', app);
 exports.$set('onInstallStateResponse', onInstallStateResponse);