Rename AllocationSite::payload to AllocationSite::transition_info

BUG=
R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/18749004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15556 ce2b1a6d-e550-0410-aec6-3dcde31c8c00