Expose Service Describer in Dart mojo package

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

Index: mojo/dart/packages/mojo_services/lib/vsync/vsync.mojom.dart
diff --git a/mojo/dart/packages/mojo_services/lib/vsync/vsync.mojom.dart b/mojo/dart/packages/mojo_services/lib/vsync/vsync.mojom.dart
index 9398004b344734f78bc1db906e629ecd150512d3..e8af445b7e6875e98d0cd29b6abf14df483e9b39 100644
--- a/mojo/dart/packages/mojo_services/lib/vsync/vsync.mojom.dart
+++ b/mojo/dart/packages/mojo_services/lib/vsync/vsync.mojom.dart
@@ -152,11 +152,14 @@ const int _VSyncProvider_awaitVSyncName = 0;
 
 
 class _VSyncProviderServiceDescription 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 VSyncProvider {
@@ -368,7 +371,7 @@ class VSyncProviderStub extends bindings.Stub {
 
   int get version => 0;
 
-  service_describer.ServiceDescription get serviceDescription =>
+  static service_describer.ServiceDescription get serviceDescription =>
     new _VSyncProviderServiceDescription();
 }