Expose Service Describer in Dart mojo package

mojo/dart/packages/mojo/lib/mojo/application.mojom.dart

Index: mojo/dart/packages/mojo/lib/mojo/application.mojom.dart
diff --git a/mojo/dart/packages/mojo/lib/mojo/application.mojom.dart b/mojo/dart/packages/mojo/lib/mojo/application.mojom.dart
index c2fb11a3f71ca3fcadd196cbc50992d484c05221..724bc81dcf03791a37f69b8865b33064191f7475 100644
--- a/mojo/dart/packages/mojo/lib/mojo/application.mojom.dart
+++ b/mojo/dart/packages/mojo/lib/mojo/application.mojom.dart
@@ -310,11 +310,14 @@ const int _Application_requestQuitName = 2;
 
 
 class _ApplicationServiceDescription 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 Application {
@@ -519,7 +522,7 @@ class ApplicationStub extends bindings.Stub {
 
   int get version => 0;
 
-  service_describer.ServiceDescription get serviceDescription =>
+  static service_describer.ServiceDescription get serviceDescription =>
     new _ApplicationServiceDescription();
 }