Expose Service Describer in Dart mojo package

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

Index: mojo/dart/packages/mojo_services/lib/mojo/http_server.mojom.dart
diff --git a/mojo/dart/packages/mojo_services/lib/mojo/http_server.mojom.dart b/mojo/dart/packages/mojo_services/lib/mojo/http_server.mojom.dart
index eca6cc3d7cc34b5a7b342abc576ac5c195b9f357..eff21c420066d455cfc2cb44b63094bc9e51f123 100644
--- a/mojo/dart/packages/mojo_services/lib/mojo/http_server.mojom.dart
+++ b/mojo/dart/packages/mojo_services/lib/mojo/http_server.mojom.dart
@@ -105,11 +105,14 @@ const int _HttpServerDelegate_onConnectedName = 0;
 
 
 class _HttpServerDelegateServiceDescription 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 HttpServerDelegate {
@@ -281,8 +284,13 @@ class HttpServerDelegateStub extends bindings.Stub {
 
   int get version => 0;
 
-  service_describer.ServiceDescription get serviceDescription =>
-    new _HttpServerDelegateServiceDescription();
+  static service_describer.ServiceDescription _cachedServiceDescription;
+  static service_describer.ServiceDescription get serviceDescription {
+    if (_cachedServiceDescription == null) {
+      _cachedServiceDescription = new _HttpServerDelegateServiceDescription();
+    }
+    return _cachedServiceDescription;
+  }
 }