Expose Service Describer in Dart mojo package

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

Index: mojo/dart/packages/mojo_services/lib/mojo/ui/view_trees.mojom.dart
diff --git a/mojo/dart/packages/mojo_services/lib/mojo/ui/view_trees.mojom.dart b/mojo/dart/packages/mojo_services/lib/mojo/ui/view_trees.mojom.dart
index 9cc565e69d658cc43eb7dbe207268f52b6945071..4c776cef584a663e3ca2e24ba2a310a9333a914d 100644
--- a/mojo/dart/packages/mojo_services/lib/mojo/ui/view_trees.mojom.dart
+++ b/mojo/dart/packages/mojo_services/lib/mojo/ui/view_trees.mojom.dart
@@ -927,11 +927,14 @@ const int _ViewTree_onRootUnavailableName = 1;
 
 
 class _ViewTreeServiceDescription 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 ViewTree {
@@ -1198,8 +1201,13 @@ class ViewTreeStub extends bindings.Stub {
 
   int get version => 0;
 
-  service_describer.ServiceDescription get serviceDescription =>
-    new _ViewTreeServiceDescription();
+  static service_describer.ServiceDescription _cachedServiceDescription;
+  static service_describer.ServiceDescription get serviceDescription {
+    if (_cachedServiceDescription == null) {
+      _cachedServiceDescription = new _ViewTreeServiceDescription();
+    }
+    return _cachedServiceDescription;
+  }
 }
 
 const int _ViewTreeHost_getTokenName = 0;
@@ -1212,11 +1220,14 @@ const int _ViewTreeHost_layoutRootName = 5;
 
 
 class _ViewTreeHostServiceDescription 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 ViewTreeHost {
@@ -1545,8 +1556,13 @@ class ViewTreeHostStub extends bindings.Stub {
 
   int get version => 0;
 
-  service_describer.ServiceDescription get serviceDescription =>
-    new _ViewTreeHostServiceDescription();
+  static service_describer.ServiceDescription _cachedServiceDescription;
+  static service_describer.ServiceDescription get serviceDescription {
+    if (_cachedServiceDescription == null) {
+      _cachedServiceDescription = new _ViewTreeHostServiceDescription();
+    }
+    return _cachedServiceDescription;
+  }
 }