Expose Service Describer in Dart mojo package

mojo/dart/packages/mojo_services/lib/mojo/ui/input_dispatcher.mojom.dart

Index: mojo/dart/packages/mojo_services/lib/mojo/ui/input_dispatcher.mojom.dart
diff --git a/mojo/dart/packages/mojo_services/lib/mojo/ui/input_dispatcher.mojom.dart b/mojo/dart/packages/mojo_services/lib/mojo/ui/input_dispatcher.mojom.dart
index 9abc7ab8195ff7f431f2dcec32b0770360c0ef65..33d915fb067f8fbc55882b33959dec49cbc5ebfc 100644
--- a/mojo/dart/packages/mojo_services/lib/mojo/ui/input_dispatcher.mojom.dart
+++ b/mojo/dart/packages/mojo_services/lib/mojo/ui/input_dispatcher.mojom.dart
@@ -94,11 +94,14 @@ const int _InputDispatcher_dispatchEventName = 0;
 
 
 class _InputDispatcherServiceDescription 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 InputDispatcher {
@@ -269,8 +272,13 @@ class InputDispatcherStub extends bindings.Stub {
 
   int get version => 0;
 
-  service_describer.ServiceDescription get serviceDescription =>
-    new _InputDispatcherServiceDescription();
+  static service_describer.ServiceDescription _cachedServiceDescription;
+  static service_describer.ServiceDescription get serviceDescription {
+    if (_cachedServiceDescription == null) {
+      _cachedServiceDescription = new _InputDispatcherServiceDescription();
+    }
+    return _cachedServiceDescription;
+  }
 }