Expose Service Describer in Dart mojo package

mojo/dart/packages/mojo_services/lib/mojo/gfx/composition/resources.mojom.dart

Index: mojo/dart/packages/mojo_services/lib/mojo/gfx/composition/resources.mojom.dart
diff --git a/mojo/dart/packages/mojo_services/lib/mojo/gfx/composition/resources.mojom.dart b/mojo/dart/packages/mojo_services/lib/mojo/gfx/composition/resources.mojom.dart
index 9714091b3423f55eb1d6f88af85a5a57896423d1..1f155413d0b94a86401b163bd463f80d6cb62f2d 100644
--- a/mojo/dart/packages/mojo_services/lib/mojo/gfx/composition/resources.mojom.dart
+++ b/mojo/dart/packages/mojo_services/lib/mojo/gfx/composition/resources.mojom.dart
@@ -375,11 +375,14 @@ const int _MailboxTextureCallback_onMailboxTextureReleasedName = 0;
 
 
 class _MailboxTextureCallbackServiceDescription 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 MailboxTextureCallback {
@@ -549,8 +552,13 @@ class MailboxTextureCallbackStub extends bindings.Stub {
 
   int get version => 0;
 
-  service_describer.ServiceDescription get serviceDescription =>
-    new _MailboxTextureCallbackServiceDescription();
+  static service_describer.ServiceDescription _cachedServiceDescription;
+  static service_describer.ServiceDescription get serviceDescription {
+    if (_cachedServiceDescription == null) {
+      _cachedServiceDescription = new _MailboxTextureCallbackServiceDescription();
+    }
+    return _cachedServiceDescription;
+  }
 }