Expose Service Describer in Dart mojo package

mojo/dart/packages/mojo_services/lib/mojo/gfx/composition/scheduling.mojom.dart

Index: mojo/dart/packages/mojo_services/lib/mojo/gfx/composition/scheduling.mojom.dart
diff --git a/mojo/dart/packages/mojo_services/lib/mojo/gfx/composition/scheduling.mojom.dart b/mojo/dart/packages/mojo_services/lib/mojo/gfx/composition/scheduling.mojom.dart
index ea330fec3f32bcbe8247d82392b6e13987d5d687..6705211437f841deb28e29e3bcc375b86c5f6415 100644
--- a/mojo/dart/packages/mojo_services/lib/mojo/gfx/composition/scheduling.mojom.dart
+++ b/mojo/dart/packages/mojo_services/lib/mojo/gfx/composition/scheduling.mojom.dart
@@ -269,11 +269,14 @@ const int _SceneScheduler_scheduleFrameName = 0;
 
 
 class _SceneSchedulerServiceDescription 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 SceneScheduler {
@@ -485,8 +488,13 @@ class SceneSchedulerStub extends bindings.Stub {
 
   int get version => 0;
 
-  service_describer.ServiceDescription get serviceDescription =>
-    new _SceneSchedulerServiceDescription();
+  static service_describer.ServiceDescription _cachedServiceDescription;
+  static service_describer.ServiceDescription get serviceDescription {
+    if (_cachedServiceDescription == null) {
+      _cachedServiceDescription = new _SceneSchedulerServiceDescription();
+    }
+    return _cachedServiceDescription;
+  }
 }