Expose Service Describer in Dart mojo package

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

Index: mojo/dart/packages/mojo_services/lib/mojo/gfx/composition/hit_tests.mojom.dart
diff --git a/mojo/dart/packages/mojo_services/lib/mojo/gfx/composition/hit_tests.mojom.dart b/mojo/dart/packages/mojo_services/lib/mojo/gfx/composition/hit_tests.mojom.dart
index acc0c0a840f23d14768cd95e9a9a1daf59f37db6..f3fef4a64b25edbceef73d8fb27fe3be3e3d7703 100644
--- a/mojo/dart/packages/mojo_services/lib/mojo/gfx/composition/hit_tests.mojom.dart
+++ b/mojo/dart/packages/mojo_services/lib/mojo/gfx/composition/hit_tests.mojom.dart
@@ -393,11 +393,14 @@ const int _HitTester_hitTestName = 0;
 
 
 class _HitTesterServiceDescription 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 HitTester {
@@ -610,8 +613,13 @@ class HitTesterStub extends bindings.Stub {
 
   int get version => 0;
 
-  service_describer.ServiceDescription get serviceDescription =>
-    new _HitTesterServiceDescription();
+  static service_describer.ServiceDescription _cachedServiceDescription;
+  static service_describer.ServiceDescription get serviceDescription {
+    if (_cachedServiceDescription == null) {
+      _cachedServiceDescription = new _HitTesterServiceDescription();
+    }
+    return _cachedServiceDescription;
+  }
 }