Fixes the debug check failure on sorting an object with an array __proto__.

Original Issue: https://codereview.chromium.org/14779011/

TBR=adamk@chromium.org

Review URL: https://codereview.chromium.org/14977015

Patch from Rafael Weinstein <rafaelw@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14698 ce2b1a6d-e550-0410-aec6-3dcde31c8c00