Expose Service Describer in Dart mojo package

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

Index: mojo/dart/packages/mojo_services/lib/contacts/contacts.mojom.dart
diff --git a/mojo/dart/packages/mojo_services/lib/contacts/contacts.mojom.dart b/mojo/dart/packages/mojo_services/lib/contacts/contacts.mojom.dart
index 588de1c4d685be8a38ba206e0f5be16e7de0a155..0df37ffcea448ba22895178dfd208cd8d4d9b136 100644
--- a/mojo/dart/packages/mojo_services/lib/contacts/contacts.mojom.dart
+++ b/mojo/dart/packages/mojo_services/lib/contacts/contacts.mojom.dart
@@ -774,11 +774,14 @@ const int _ContactsService_getPhotoName = 3;
 
 
 class _ContactsServiceServiceDescription 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 ContactsService {
@@ -1165,8 +1168,13 @@ class ContactsServiceStub extends bindings.Stub {
 
   int get version => 0;
 
-  service_describer.ServiceDescription get serviceDescription =>
-    new _ContactsServiceServiceDescription();
+  static service_describer.ServiceDescription _cachedServiceDescription;
+  static service_describer.ServiceDescription get serviceDescription {
+    if (_cachedServiceDescription == null) {
+      _cachedServiceDescription = new _ContactsServiceServiceDescription();
+    }
+    return _cachedServiceDescription;
+  }
 }