Tighten HAS_PRIVATE to own properties

R=mstarzinger@chromium.org
BUG=

Review URL: https://codereview.chromium.org/290373002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21379 ce2b1a6d-e550-0410-aec6-3dcde31c8c00