space. This is useful because the unrooted mementos affect heap
decisions like pretenuring mode, and helps to gauge the effectiveness
of allocation-site feedback.

R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/25273002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@17027 ce2b1a6d-e550-0410-aec6-3dcde31c8c00