Expose Service Describer in Dart mojo package

mojo/dart/packages/mojo_services/lib/mojo/clipboard.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 clipboard_mojom;
 
 import 'dart:async';
 
 import 'package:mojo/bindings.dart' as bindings;
 import 'package:mojo/core.dart' as core;
@@ skipping 695 matching lines @@
   }
 
   int toJson() => mojoEnumValue;
 }
 
 
 
 
 
 class _ClipboardServiceDescription 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 Clipboard {
   static const String serviceName = "mojo::Clipboard";
   dynamic getSequenceNumber(ClipboardType clipboardType,[Function responseFactory = null]);
   dynamic getAvailableMimeTypes(ClipboardType clipboardTypes,[Function responseFactory = null]);
   dynamic readMimeType(ClipboardType clipboardType,String mimeType,[Function responseFactory = null]);
   void writeClipboardData(ClipboardType clipboardType, Map<String, List<int>> data);
   static const String mimeTypeText = "text/plain";
   static const String mimeTypeHtml = "text/html";
@@ skipping 326 matching lines @@
     _impl = d;
   }
 
   String toString() {
     var superString = super.toString();
     return "ClipboardStub($superString)";
   }
 
   int get version => 0;
 
-  service_describer.ServiceDescription get serviceDescription =>
-    new _ClipboardServiceDescription();
+  static service_describer.ServiceDescription _cachedServiceDescription;
+  static service_describer.ServiceDescription get serviceDescription {
+    if (_cachedServiceDescription == null) {
+      _cachedServiceDescription = new _ClipboardServiceDescription();
+    }
+    return _cachedServiceDescription;
+  }
 }