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

src/runtime/runtime-array.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/runtime/runtime-utils.h"
 
 #include "src/arguments.h"
 #include "src/code-stubs.h"
 #include "src/conversions-inl.h"
 #include "src/elements.h"
@@ skipping 69 matching lines @@
   CONVERT_SMI_ARG_CHECKED(index, 1);
   CONVERT_ARG_CHECKED(Object, value, 2);
   object->set(index, value);
   return isolate->heap()->undefined_value();
 }
 
 
 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);
   return *object;
 }
 
 
 // Moves all own elements of an object, that are below a limit, to positions
 // starting at zero. All undefined values are placed after non-undefined values,
 // and are followed by non-existing element. Does not change the length
@@ skipping 333 matching lines @@
 RUNTIME_FUNCTION(Runtime_ArraySpeciesConstructor) {
   HandleScope scope(isolate);
   DCHECK(args.length() == 1);
   CONVERT_ARG_HANDLE_CHECKED(Object, original_array, 0);
   RETURN_RESULT_OR_FAILURE(
       isolate, Object::ArraySpeciesConstructor(isolate, original_array));
 }
 
 }  // namespace internal
 }  // namespace v8