[turbofan] more verification of rpo

R=titzer@chromium.org

BUG=

Review URL: https://codereview.chromium.org/603533002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24630 ce2b1a6d-e550-0410-aec6-3dcde31c8c00