Landing: [hydrogen] optimize switch with string clauses. Patch by Fedor Indutny <fedor.indutny@gmail.com>.

Original code review: http://codereview.chromium.org/8373029/
Review URL: http://codereview.chromium.org/8589019

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10019 ce2b1a6d-e550-0410-aec6-3dcde31c8c00