Lazy load chrome.* APIs

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 bindings for the app API.
+// Custom binding for the app API.
 
 var appNatives = requireNative('app');
+var chrome = requireNative('chrome').GetChrome();
+var GetAvailability = requireNative('v8_context').GetAvailability;
+var DCHECK = requireNative('logging').DCHECK;
 
 // This becomes chrome.app
 var app = {
   getIsInstalled: appNatives.GetIsInstalled,
   install: appNatives.Install,
   getDetails: appNatives.GetDetails,
   getDetailsForFrame: appNatives.GetDetailsForFrame,
   runningState: 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', appNatives.GetIsInstalled);
 
-// Called by app_bindings.cc.
+// Called by app_binding.cc.
 // This becomes chromeHidden.app
 var chromeHiddenApp = {
   onGetAppNotifyChannelResponse: function(channelId, error, callbackId) {
     if (callbackId) {
       callbacks[callbackId](channelId, error);
       delete callbacks[callbackId];
     }
   },
 
   onInstallStateResponse: function(state, callbackId) {
     if (callbackId) {
       callbacks[callbackId](state);
       delete callbacks[callbackId];
     }
   }
 };
 
 // appNotification stuff.
 //
-// TODO(kalman): move this stuff to its own custom bindings.
+// TODO(kalman): move this stuff to its own custom binding.
 // It will be bit tricky since I'll need to look into why there are
 // permissions defined for app notifications, yet this always sets it up?
 var callbacks = {};
 var nextCallbackId = 1;
 
 // This becomes chrome.appNotifications.
 var appNotifications = {
   getChannel: function getChannel(clientId, callback) {
     var callbackId = 0;
     if (callback) {
       callbackId = nextCallbackId++;
       callbacks[callbackId] = callback;
     }
     appNatives.GetAppNotifyChannel(clientId, callbackId);
   }
 };
 
 app.installState = function getInstallState(callback) {
   var callbackId = nextCallbackId++;
   callbacks[callbackId] = callback;
   appNatives.GetInstallState(callbackId);
 };
 
-// These must match the names in InstallAppBindings() in
+function defineCheckAvailabilityGetter(name, apiName, target) {

[not at google - send to devlin, 2013/02/13 01:45:49]

defineLazyGetter?

Comment why it's necessary?

[cduvall, 2013/02/15 00:40:28]

This actually doesn't need the lazy getter anymore.

+  exports.__defineGetter__(name, function() {
+    var availability = GetAvailability(apiName);
+    if (!availability.is_available) {
+      // If this API is not available, return undefined. An exception is not
+      // thrown like the other APIs because it is not guaranteed that this will
+      // be loaded in a try catch block.
+      return;

[not at google - send to devlin, 2013/02/13 01:45:49]

might as well say return undefined;

[cduvall, 2013/02/15 00:40:28]

Done.

+    }
+    return target;
+  });
+}
+
+// These must match the names in InstallAppbinding() in
 // chrome/renderer/extensions/dispatcher.cc.
-exports.chromeApp = app;
-exports.chromeAppNotifications = appNotifications;
-exports.chromeHiddenApp = chromeHiddenApp;
+defineCheckAvailabilityGetter('chromeApp', 'app', app);
+defineCheckAvailabilityGetter('chromeAppNotifications',
+                              'app',
+                               appNotifications);
+defineCheckAvailabilityGetter('chromeHiddenApp', 'app', chromeHiddenApp);