occur only when custom feedback needs to be gathered (future CLs).

Now rebased on https://codereview.chromium.org/254623002/, which moves the type feedback vector to the SharedFunctionInfo.

R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/247373002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@21093 ce2b1a6d-e550-0410-aec6-3dcde31c8c00