Refactor ScriptData class for cached compile data.

R=marja@chromium.org, vogelheim@chromium.org

Review URL: https://codereview.chromium.org/376223002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22314 ce2b1a6d-e550-0410-aec6-3dcde31c8c00