Expose Service Describer in Dart mojo package

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

Index: mojo/dart/packages/mojo_services/lib/mojo/host_resolver.mojom.dart
diff --git a/mojo/dart/packages/mojo_services/lib/mojo/host_resolver.mojom.dart b/mojo/dart/packages/mojo_services/lib/mojo/host_resolver.mojom.dart
index 3f6d8afb497c289eea4bd2ffa138d922e07fc951..a20944701bd3f18c307666e44d72ad24f9b71cd0 100644
--- a/mojo/dart/packages/mojo_services/lib/mojo/host_resolver.mojom.dart
+++ b/mojo/dart/packages/mojo_services/lib/mojo/host_resolver.mojom.dart
@@ -219,11 +219,14 @@ const int _HostResolver_getHostAddressesName = 0;
 
 
 class _HostResolverServiceDescription 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 HostResolver {
@@ -438,7 +441,7 @@ class HostResolverStub extends bindings.Stub {
 
   int get version => 0;
 
-  service_describer.ServiceDescription get serviceDescription =>
+  static service_describer.ServiceDescription get serviceDescription =>
     new _HostResolverServiceDescription();
 }