Expose Service Describer in Dart mojo package

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

Index: mojo/dart/packages/mojo_services/lib/mojo/cookie_store.mojom.dart
diff --git a/mojo/dart/packages/mojo_services/lib/mojo/cookie_store.mojom.dart b/mojo/dart/packages/mojo_services/lib/mojo/cookie_store.mojom.dart
index d676d185cdfd14706d6bc61ddaa2ddcf377b2b63..4f64f1718dc01f0b2843c80be3de4c1db83ce365 100644
--- a/mojo/dart/packages/mojo_services/lib/mojo/cookie_store.mojom.dart
+++ b/mojo/dart/packages/mojo_services/lib/mojo/cookie_store.mojom.dart
@@ -329,11 +329,14 @@ const int _CookieStore_setName = 1;
 
 
 class _CookieStoreServiceDescription 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 CookieStore {
@@ -604,8 +607,13 @@ class CookieStoreStub extends bindings.Stub {
 
   int get version => 0;
 
-  service_describer.ServiceDescription get serviceDescription =>
-    new _CookieStoreServiceDescription();
+  static service_describer.ServiceDescription _cachedServiceDescription;
+  static service_describer.ServiceDescription get serviceDescription {
+    if (_cachedServiceDescription == null) {
+      _cachedServiceDescription = new _CookieStoreServiceDescription();
+    }
+    return _cachedServiceDescription;
+  }
 }