The only ways we use this class require it, as multiple isolates can race
to initialize data structures. This showed up as intermittant failures on
nosnap build bots.

R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/238973004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@20794 ce2b1a6d-e550-0410-aec6-3dcde31c8c00