Expose Service Describer in Dart mojo package

mojo/dart/packages/mojo_services/lib/authentication/authentication.mojom.dart

 // 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.
 
 library authentication_mojom;
 
 import 'dart:async';
 
 import 'package:mojo/bindings.dart' as bindings;
 import 'package:mojo/core.dart' as core;
@@ skipping 429 matching lines @@
 
 
 
 const int _AuthenticationService_selectAccountName = 0;
 const int _AuthenticationService_getOAuth2TokenName = 1;
 const int _AuthenticationService_clearOAuth2TokenName = 2;
 
 
 
 class _AuthenticationServiceServiceDescription implements service_describer.ServiceDescription {
-  dynamic getTopLevelInterface([Function responseFactory]) => null;
+  dynamic getTopLevelInterface([Function responseFactory]) =>
+      responseFactory(null);
 
-  dynamic getTypeDefinition(String typeKey, [Function responseFactory]) => null;
+  dynamic getTypeDefinition(String typeKey, [Function responseFactory]) =>
+      responseFactory(null);
 
-  dynamic getAllTypeDefinitions([Function responseFactory]) => null;
+  dynamic getAllTypeDefinitions([Function responseFactory]) =>
+      responseFactory(null);
 }
 
 abstract class AuthenticationService {
   static const String serviceName = "authentication::AuthenticationService";
   dynamic selectAccount(bool returnLastSelected,[Function responseFactory = null]);
   dynamic getOAuth2Token(String username,List<String> scopes,[Function responseFactory = null]);
   void clearOAuth2Token(String token);
 }
 
 
@@ skipping 267 matching lines @@
     _impl = d;
   }
 
   String toString() {
     var superString = super.toString();
     return "AuthenticationServiceStub($superString)";
   }
 
   int get version => 0;
 
-  service_describer.ServiceDescription get serviceDescription =>
-    new _AuthenticationServiceServiceDescription();
+  static service_describer.ServiceDescription _cachedServiceDescription;
+  static service_describer.ServiceDescription get serviceDescription {
+    if (_cachedServiceDescription == null) {
+      _cachedServiceDescription = new _AuthenticationServiceServiceDescription();
+    }
+    return _cachedServiceDescription;
+  }
 }