Revert API change from issue 1053883002.

sky/framework/embedder.dart

Index: sky/framework/embedder.dart
diff --git a/sky/framework/embedder.dart b/sky/framework/embedder.dart
index 4ebd9f64d78483694999e82d96bb194c71bd9fd1..d91f8c4e15b1c74b95d9d06bb615a65382e12c5a 100644
--- a/sky/framework/embedder.dart
+++ b/sky/framework/embedder.dart
@@ -50,11 +50,11 @@ class _EmbedderImpl {
     appSp.close();
   }
 
-  ServiceRegistry get serviceRegistry {
+  ServiceRegistryProxy get serviceRegistry {
     if (_serviceRegistry == null) {
       _serviceRegistry = new ServiceRegistryProxy.fromHandle(
           new core.MojoHandle(internals.takeServiceRegistry()));
     }
-    return _serviceRegistry.ptr;
+    return _serviceRegistry;
   }
 }