Expose Service Describer in Dart mojo package

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

Index: mojo/dart/packages/mojo_services/lib/mojo/tcp_server_socket.mojom.dart
diff --git a/mojo/dart/packages/mojo_services/lib/mojo/tcp_server_socket.mojom.dart b/mojo/dart/packages/mojo_services/lib/mojo/tcp_server_socket.mojom.dart
index a1a5586cd7dcc391b1e32318e8b9796d35f4db34..334929fb961fea566ecd6953b5b2c627c118bec1 100644
--- a/mojo/dart/packages/mojo_services/lib/mojo/tcp_server_socket.mojom.dart
+++ b/mojo/dart/packages/mojo_services/lib/mojo/tcp_server_socket.mojom.dart
@@ -210,11 +210,14 @@ const int _TcpServerSocket_acceptName = 0;
 
 
 class _TcpServerSocketServiceDescription 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 TcpServerSocket {
@@ -430,8 +433,13 @@ class TcpServerSocketStub extends bindings.Stub {
 
   int get version => 0;
 
-  service_describer.ServiceDescription get serviceDescription =>
-    new _TcpServerSocketServiceDescription();
+  static service_describer.ServiceDescription _cachedServiceDescription;
+  static service_describer.ServiceDescription get serviceDescription {
+    if (_cachedServiceDescription == null) {
+      _cachedServiceDescription = new _TcpServerSocketServiceDescription();
+    }
+    return _cachedServiceDescription;
+  }
 }