This change preserves the contents of optimized code maps during GCs but
treats the references in this cache weakly. It uses infrastructure from
code flushing to maintain a list of all caches.

R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/14794007

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14695 ce2b1a6d-e550-0410-aec6-3dcde31c8c00