Make freeze & friends ignore private properties

R=verwaest@chromium.org
BUG=v8:3419
LOG=Y

Review URL: https://codereview.chromium.org/355123006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22132 ce2b1a6d-e550-0410-aec6-3dcde31c8c00