Expose Service Describer in Dart mojo package

mojo/dart/packages/_mojo_for_test_only/lib/test/echo_service.mojom.dart

Index: mojo/dart/packages/_mojo_for_test_only/lib/test/echo_service.mojom.dart
diff --git a/mojo/dart/packages/_mojo_for_test_only/lib/test/echo_service.mojom.dart b/mojo/dart/packages/_mojo_for_test_only/lib/test/echo_service.mojom.dart
index 7e5992fa3da274cd5573f30c02e2ac6bbc56c07a..f35f65d95cd1371d3a22f56ffaba7b7c0911daf9 100644
--- a/mojo/dart/packages/_mojo_for_test_only/lib/test/echo_service.mojom.dart
+++ b/mojo/dart/packages/_mojo_for_test_only/lib/test/echo_service.mojom.dart
@@ -480,13 +480,13 @@ mojom_types.MojomInterface _echoServiceEchoService() {
 
 class _EchoServiceServiceDescription implements service_describer.ServiceDescription {
   dynamic getTopLevelInterface([Function responseFactory]) =>
-      _echoServiceEchoService();
+    responseFactory(_echoServiceEchoService());
 
   dynamic getTypeDefinition(String typeKey, [Function responseFactory]) =>
-      getAllMojomTypeDefinitions()[typeKey];
+    responseFactory(getAllMojomTypeDefinitions()[typeKey]);
 
   dynamic getAllTypeDefinitions([Function responseFactory]) =>
-      getAllMojomTypeDefinitions();
+    responseFactory(getAllMojomTypeDefinitions());
 }
 
 abstract class EchoService {
@@ -771,7 +771,7 @@ class EchoServiceStub extends bindings.Stub {
 
   int get version => 0;
 
-  service_describer.ServiceDescription get serviceDescription =>
+  static service_describer.ServiceDescription get serviceDescription =>
     new _EchoServiceServiceDescription();
 }