Use symbols instead of hidden properties for i18n markers.

src/runtime/runtime.cc

Index: src/runtime/runtime.cc
diff --git a/src/runtime/runtime.cc b/src/runtime/runtime.cc
index dbb51ec926f7e1b29b66d7e275216c4149f172c7..30497923f6f26e23a3f3b28ffb2bb983660fb2a6 100644
--- a/src/runtime/runtime.cc
+++ b/src/runtime/runtime.cc
@@ -1040,18 +1040,6 @@ MaybeHandle<Object> Runtime::DeleteObjectProperty(Isolate* isolate,
 }
 
 
-RUNTIME_FUNCTION(Runtime_SetHiddenProperty) {
-  HandleScope scope(isolate);
-  RUNTIME_ASSERT(args.length() == 3);
-
-  CONVERT_ARG_HANDLE_CHECKED(JSObject, object, 0);
-  CONVERT_ARG_HANDLE_CHECKED(String, key, 1);
-  CONVERT_ARG_HANDLE_CHECKED(Object, value, 2);
-  RUNTIME_ASSERT(key->IsUniqueName());
-  return *JSObject::SetHiddenProperty(object, key, value);
-}
-
-
 RUNTIME_FUNCTION(Runtime_AddNamedProperty) {
   HandleScope scope(isolate);
   RUNTIME_ASSERT(args.length() == 4);