Switch transition zapping to slower version.

This is just an experiment to track down high crash rates on some
systems where third-party software corrupts memory regions.

R=danno@chromium.org

Review URL: https://codereview.chromium.org/13630002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14134 ce2b1a6d-e550-0410-aec6-3dcde31c8c00