Allocation site pretenuring.

Pretenuring decisions are made based on allocation site lifetime statistics.

BUG=
R=mstarzinger@chromium.org, mvstanton@chromium.org

Review URL: https://codereview.chromium.org/96783002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18532 ce2b1a6d-e550-0410-aec6-3dcde31c8c00