Added checked convert of object to DefineOrRedefineAccessorProperty.

src/runtime.cc

Index: src/runtime.cc
===================================================================
--- src/runtime.cc	(revision 3802)
+++ src/runtime.cc	(working copy)
@@ -2891,7 +2891,7 @@
 static Object* Runtime_DefineOrRedefineAccessorProperty(Arguments args) {
   ASSERT(args.length() == 5);
   HandleScope scope;
-  Handle<JSObject> obj = args.at<JSObject>(0);
+  CONVERT_ARG_CHECKED(JSObject, obj, 0);
   CONVERT_CHECKED(String, name, args[1]);
   CONVERT_CHECKED(Smi, flag_setter, args[2]);
   CONVERT_CHECKED(JSFunction, fun, args[3]);