Expose Service Describer in Dart mojo package

mojo/dart/packages/mojo/lib/mojo/shell.mojom.dart

Index: mojo/dart/packages/mojo/lib/mojo/shell.mojom.dart
diff --git a/mojo/dart/packages/mojo/lib/mojo/shell.mojom.dart b/mojo/dart/packages/mojo/lib/mojo/shell.mojom.dart
index 83d9d6d6cdb2f553e6f394ec71bf91e21379dc65..b170aab4e0136d81c2976fe8852520d0c8c5b4ac 100644
--- a/mojo/dart/packages/mojo/lib/mojo/shell.mojom.dart
+++ b/mojo/dart/packages/mojo/lib/mojo/shell.mojom.dart
@@ -193,11 +193,14 @@ const int _Shell_createApplicationConnectorName = 1;
 
 
 class _ShellServiceDescription 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 Shell {
@@ -385,7 +388,7 @@ class ShellStub extends bindings.Stub {
 
   int get version => 0;
 
-  service_describer.ServiceDescription get serviceDescription =>
+  static service_describer.ServiceDescription get serviceDescription =>
     new _ShellServiceDescription();
 }