Expose Service Describer in Dart mojo package

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

Index: mojo/dart/packages/mojo_services/lib/mojo/ui/view_provider.mojom.dart
diff --git a/mojo/dart/packages/mojo_services/lib/mojo/ui/view_provider.mojom.dart b/mojo/dart/packages/mojo_services/lib/mojo/ui/view_provider.mojom.dart
index 0052a86b6e82cb1259812ef79878b4a6e6bbb3ac..d9a801fe4cf6da804f68cfcf8819e561730ce179 100644
--- a/mojo/dart/packages/mojo_services/lib/mojo/ui/view_provider.mojom.dart
+++ b/mojo/dart/packages/mojo_services/lib/mojo/ui/view_provider.mojom.dart
@@ -119,11 +119,14 @@ const int _ViewProvider_createViewName = 0;
 
 
 class _ViewProviderServiceDescription 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 ViewProvider {
@@ -296,8 +299,13 @@ class ViewProviderStub extends bindings.Stub {
 
   int get version => 0;
 
-  service_describer.ServiceDescription get serviceDescription =>
-    new _ViewProviderServiceDescription();
+  static service_describer.ServiceDescription _cachedServiceDescription;
+  static service_describer.ServiceDescription get serviceDescription {
+    if (_cachedServiceDescription == null) {
+      _cachedServiceDescription = new _ViewProviderServiceDescription();
+    }
+    return _cachedServiceDescription;
+  }
 }