Expose Service Describer in Dart mojo package

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

Index: mojo/dart/packages/mojo_services/lib/mojo/device_info.mojom.dart
diff --git a/mojo/dart/packages/mojo_services/lib/mojo/device_info.mojom.dart b/mojo/dart/packages/mojo_services/lib/mojo/device_info.mojom.dart
index 4051d914960d7f2ad4a2c14e5d7149acb8c3906f..61dfaf9239d9f417e7b802bae0f9af217ba6a12b 100644
--- a/mojo/dart/packages/mojo_services/lib/mojo/device_info.mojom.dart
+++ b/mojo/dart/packages/mojo_services/lib/mojo/device_info.mojom.dart
@@ -245,11 +245,14 @@ class DeviceInfoDeviceType extends bindings.MojoEnum {
 
 
 class _DeviceInfoServiceDescription 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 DeviceInfo {
@@ -461,8 +464,13 @@ class DeviceInfoStub extends bindings.Stub {
 
   int get version => 0;
 
-  service_describer.ServiceDescription get serviceDescription =>
-    new _DeviceInfoServiceDescription();
+  static service_describer.ServiceDescription _cachedServiceDescription;
+  static service_describer.ServiceDescription get serviceDescription {
+    if (_cachedServiceDescription == null) {
+      _cachedServiceDescription = new _DeviceInfoServiceDescription();
+    }
+    return _cachedServiceDescription;
+  }
 }