Expose Service Describer in Dart mojo package

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

Index: mojo/dart/packages/mojo_services/lib/mojo/tcp_connected_socket.mojom.dart
diff --git a/mojo/dart/packages/mojo_services/lib/mojo/tcp_connected_socket.mojom.dart b/mojo/dart/packages/mojo_services/lib/mojo/tcp_connected_socket.mojom.dart
index b6dae397ff98857fc63ae3cf2035e42d95481615..5da844884e86b920fb6cbb1c1eacdd74261d357f 100644
--- a/mojo/dart/packages/mojo_services/lib/mojo/tcp_connected_socket.mojom.dart
+++ b/mojo/dart/packages/mojo_services/lib/mojo/tcp_connected_socket.mojom.dart
@@ -17,11 +17,14 @@ import 'package:mojo/mojo/bindings/types/service_describer.mojom.dart' as servic
 
 
 class _TcpConnectedSocketServiceDescription 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 TcpConnectedSocket {
@@ -177,8 +180,13 @@ class TcpConnectedSocketStub extends bindings.Stub {
 
   int get version => 0;
 
-  service_describer.ServiceDescription get serviceDescription =>
-    new _TcpConnectedSocketServiceDescription();
+  static service_describer.ServiceDescription _cachedServiceDescription;
+  static service_describer.ServiceDescription get serviceDescription {
+    if (_cachedServiceDescription == null) {
+      _cachedServiceDescription = new _TcpConnectedSocketServiceDescription();
+    }
+    return _cachedServiceDescription;
+  }
 }