Expose Service Describer in Dart mojo package

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

Index: mojo/dart/packages/mojo_services/lib/speech_recognizer/speech_recognizer.mojom.dart
diff --git a/mojo/dart/packages/mojo_services/lib/speech_recognizer/speech_recognizer.mojom.dart b/mojo/dart/packages/mojo_services/lib/speech_recognizer/speech_recognizer.mojom.dart
index c756e5beaa01b365fd9bfbb1db3203e5f1f704dc..3ce23f7a0ec3a167fc2bddfcc78e26d256becc7d 100644
--- a/mojo/dart/packages/mojo_services/lib/speech_recognizer/speech_recognizer.mojom.dart
+++ b/mojo/dart/packages/mojo_services/lib/speech_recognizer/speech_recognizer.mojom.dart
@@ -533,11 +533,14 @@ const int _SpeechRecognizerService_stopListeningName = 1;
 
 
 class _SpeechRecognizerServiceServiceDescription 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 SpeechRecognizerService {
@@ -763,8 +766,13 @@ class SpeechRecognizerServiceStub extends bindings.Stub {
 
   int get version => 0;
 
-  service_describer.ServiceDescription get serviceDescription =>
-    new _SpeechRecognizerServiceServiceDescription();
+  static service_describer.ServiceDescription _cachedServiceDescription;
+  static service_describer.ServiceDescription get serviceDescription {
+    if (_cachedServiceDescription == null) {
+      _cachedServiceDescription = new _SpeechRecognizerServiceServiceDescription();
+    }
+    return _cachedServiceDescription;
+  }
 }