Expose Service Describer in Dart mojo package

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

Index: mojo/dart/packages/mojo_services/lib/mojo/files/files.mojom.dart
diff --git a/mojo/dart/packages/mojo_services/lib/mojo/files/files.mojom.dart b/mojo/dart/packages/mojo_services/lib/mojo/files/files.mojom.dart
index 7df7de3b4a7a0aa57d09d2fdd6f759cfce524e6b..8987606f527a61d63bd34d8b43d4e90ec03eabef 100644
--- a/mojo/dart/packages/mojo_services/lib/mojo/files/files.mojom.dart
+++ b/mojo/dart/packages/mojo_services/lib/mojo/files/files.mojom.dart
@@ -184,11 +184,14 @@ const int _Files_openFileSystemName = 0;
 
 
 class _FilesServiceDescription 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 Files {
@@ -402,8 +405,13 @@ class FilesStub extends bindings.Stub {
 
   int get version => 0;
 
-  service_describer.ServiceDescription get serviceDescription =>
-    new _FilesServiceDescription();
+  static service_describer.ServiceDescription _cachedServiceDescription;
+  static service_describer.ServiceDescription get serviceDescription {
+    if (_cachedServiceDescription == null) {
+      _cachedServiceDescription = new _FilesServiceDescription();
+    }
+    return _cachedServiceDescription;
+  }
 }