Expose Service Describer in Dart mojo package

mojo/dart/packages/mojo_services/lib/mojo/ui/view_manager.mojom.dart

Index: mojo/dart/packages/mojo_services/lib/mojo/ui/view_manager.mojom.dart
diff --git a/mojo/dart/packages/mojo_services/lib/mojo/ui/view_manager.mojom.dart b/mojo/dart/packages/mojo_services/lib/mojo/ui/view_manager.mojom.dart
index 6c95ce3e74a2aabb647b76f1e5b201b58ab0b602..d661df120565bdb2f31680b1ccf5f5da8f19f145 100644
--- a/mojo/dart/packages/mojo_services/lib/mojo/ui/view_manager.mojom.dart
+++ b/mojo/dart/packages/mojo_services/lib/mojo/ui/view_manager.mojom.dart
@@ -234,11 +234,14 @@ const int _ViewManager_registerViewTreeName = 1;
 
 
 class _ViewManagerServiceDescription 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 ViewManager {
@@ -429,8 +432,13 @@ class ViewManagerStub extends bindings.Stub {
 
   int get version => 0;
 
-  service_describer.ServiceDescription get serviceDescription =>
-    new _ViewManagerServiceDescription();
+  static service_describer.ServiceDescription _cachedServiceDescription;
+  static service_describer.ServiceDescription get serviceDescription {
+    if (_cachedServiceDescription == null) {
+      _cachedServiceDescription = new _ViewManagerServiceDescription();
+    }
+    return _cachedServiceDescription;
+  }
 }