Expose Service Describer in Dart mojo package

mojo/dart/packages/mojo_services/lib/mojo/files/file.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 file_mojom;
 
 import 'dart:async';
 
 import 'package:mojo/bindings.dart' as bindings;
 import 'package:mojo/core.dart' as core;
@@ skipping 2377 matching lines @@
 const int _File_truncateName = 8;
 const int _File_touchName = 9;
 const int _File_dupName = 10;
 const int _File_reopenName = 11;
 const int _File_asBufferName = 12;
 const int _File_ioctlName = 13;
 
 
 
 class _FileServiceDescription 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 File {
   static const String serviceName = null;
   dynamic close([Function responseFactory = null]);
   dynamic read(int numBytesToRead,int offset,types_mojom.Whence whence,[Function responseFactory = null]);
   dynamic write(List<int> bytesToWrite,int offset,types_mojom.Whence whence,[Function responseFactory = null]);
   dynamic readToStream(core.MojoDataPipeProducer source,int offset,types_mojom.Whence whence,int numBytesToRead,[Function responseFactory = null]);
   dynamic writeFromStream(core.MojoDataPipeConsumer sink,int offset,types_mojom.Whence whence,[Function responseFactory = null]);
   dynamic tell([Function responseFactory = null]);
@@ skipping 949 matching lines @@
     _impl = d;
   }
 
   String toString() {
     var superString = super.toString();
     return "FileStub($superString)";
   }
 
   int get version => 0;
 
-  service_describer.ServiceDescription get serviceDescription =>
-    new _FileServiceDescription();
+  static service_describer.ServiceDescription _cachedServiceDescription;
+  static service_describer.ServiceDescription get serviceDescription {
+    if (_cachedServiceDescription == null) {
+      _cachedServiceDescription = new _FileServiceDescription();
+    }
+    return _cachedServiceDescription;
+  }
 }