Allow extension APIs to be called from WebUI.

extensions/renderer/resources/runtime_custom_bindings.js

 // Copyright 2014 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 runtime API.
 
 var binding = require('binding').Binding.create('runtime');
 
 var messaging = require('messaging');
 var runtimeNatives = requireNative('runtime');
@@ skipping 65 matching lines @@
 }
 
 binding.registerCustomHook(function(binding, id, contextType) {
   var apiFunctions = binding.apiFunctions;
   var runtime = binding.compiledApi;
 
   //
   // Unprivileged APIs.
   //
 
-  runtime.id = id;
+  if (id != '')
+    runtime.id = id;
 
   apiFunctions.setHandleRequest('getManifest', function() {
     return runtimeNatives.GetManifest();
   });
 
   apiFunctions.setHandleRequest('getURL', function(path) {
     path = String(path);
     if (!path.length || path[0] != '/')
       path = '/' + path;
     return 'chrome-extension://' + id + path;
@@ skipping 99 matching lines @@
       request.callback(bg);
     }
     request.callback = null;
   });
 
   bindDirectoryEntryCallback('getPackageDirectoryEntry', apiFunctions);
 });
 
 exports.bindDirectoryEntryCallback = bindDirectoryEntryCallback;
 exports.binding = binding.generate();