[runtime] %TransitionElementsKind works for any kind of JSObject.

src/runtime/runtime-array.cc

Index: src/runtime/runtime-array.cc
diff --git a/src/runtime/runtime-array.cc b/src/runtime/runtime-array.cc
index 68543d9a267c9c1473d12d3edbb89cab56a6accd..6664c814006798046ef7a6ffa279788e04146a49 100644
--- a/src/runtime/runtime-array.cc
+++ b/src/runtime/runtime-array.cc
@@ -87,7 +87,7 @@ RUNTIME_FUNCTION(Runtime_FixedArraySet) {
 RUNTIME_FUNCTION(Runtime_TransitionElementsKind) {
   HandleScope scope(isolate);
   DCHECK_EQ(2, args.length());
-  CONVERT_ARG_HANDLE_CHECKED(JSArray, object, 0);
+  CONVERT_ARG_HANDLE_CHECKED(JSObject, object, 0);
   CONVERT_ARG_HANDLE_CHECKED(Map, to_map, 1);
   ElementsKind to_kind = to_map->elements_kind();
   ElementsAccessor::ForKind(to_kind)->TransitionElementsKind(object, to_map);