- consider the source string as a special sort of back reference.
- use repeat op code for more root members.

R=mvstanton@chromium.org

Review URL: https://codereview.chromium.org/674883002

Cr-Commit-Position: refs/heads/master@{#24871}
git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24871 ce2b1a6d-e550-0410-aec6-3dcde31c8c00