Expose Service Describer in Dart mojo package

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

Index: mojo/dart/packages/mojo_services/lib/prediction/prediction.mojom.dart
diff --git a/mojo/dart/packages/mojo_services/lib/prediction/prediction.mojom.dart b/mojo/dart/packages/mojo_services/lib/prediction/prediction.mojom.dart
index b346d6e7ac4fa0e8812d2105198fd381f997a9b6..3b563b0aa11219f7bf54e0b402ab4d9c282f107b 100644
--- a/mojo/dart/packages/mojo_services/lib/prediction/prediction.mojom.dart
+++ b/mojo/dart/packages/mojo_services/lib/prediction/prediction.mojom.dart
@@ -376,11 +376,14 @@ const int _PredictionService_getPredictionListName = 0;
 
 
 class _PredictionServiceServiceDescription 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 PredictionService {
@@ -593,8 +596,13 @@ class PredictionServiceStub extends bindings.Stub {
 
   int get version => 0;
 
-  service_describer.ServiceDescription get serviceDescription =>
-    new _PredictionServiceServiceDescription();
+  static service_describer.ServiceDescription _cachedServiceDescription;
+  static service_describer.ServiceDescription get serviceDescription {
+    if (_cachedServiceDescription == null) {
+      _cachedServiceDescription = new _PredictionServiceServiceDescription();
+    }
+    return _cachedServiceDescription;
+  }
 }