Call JS functions via native context instead of js builtins object.

src/json.js

Index: src/json.js
diff --git a/src/json.js b/src/json.js
index 3bc52cbbf5dbedd475e1c2069b2e474454b8cdda..2b19e901c6486a93581080c8089931d51979d325 100644
--- a/src/json.js
+++ b/src/json.js
@@ -252,8 +252,6 @@ function JsonSerializeAdapter(key, object) {
   return JSONSerialize(key, holder, UNDEFINED, new InternalArray(), "", "");
 }
 
-utils.ExportToRuntime(function(to) {
-  to["json_serialize_adapter"] = JsonSerializeAdapter;
-});
+%ExportToRuntime(["json_serialize_adapter", JsonSerializeAdapter]);
 
 })