Expose Service Describer in Dart mojo package

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

Index: mojo/dart/packages/mojo_services/lib/mojo/tcp_bound_socket.mojom.dart
diff --git a/mojo/dart/packages/mojo_services/lib/mojo/tcp_bound_socket.mojom.dart b/mojo/dart/packages/mojo_services/lib/mojo/tcp_bound_socket.mojom.dart
index a2b057207f9f3a26953d7c8489f3e5a3393662d8..3f43074eab7c2d0da84b5910dd3682c13e4773c0 100644
--- a/mojo/dart/packages/mojo_services/lib/mojo/tcp_bound_socket.mojom.dart
+++ b/mojo/dart/packages/mojo_services/lib/mojo/tcp_bound_socket.mojom.dart
@@ -359,11 +359,14 @@ const int _TcpBoundSocket_connectName = 1;
 
 
 class _TcpBoundSocketServiceDescription 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 TcpBoundSocket {
@@ -636,8 +639,13 @@ class TcpBoundSocketStub extends bindings.Stub {
 
   int get version => 0;
 
-  service_describer.ServiceDescription get serviceDescription =>
-    new _TcpBoundSocketServiceDescription();
+  static service_describer.ServiceDescription _cachedServiceDescription;
+  static service_describer.ServiceDescription get serviceDescription {
+    if (_cachedServiceDescription == null) {
+      _cachedServiceDescription = new _TcpBoundSocketServiceDescription();
+    }
+    return _cachedServiceDescription;
+  }
 }