resource from a memory mapped file for creating strings.

Patch by Mark Lam from Hewlett-Packard Development Company, LP

Review URL: http://codereview.chromium.org/6240002/

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6386 ce2b1a6d-e550-0410-aec6-3dcde31c8c00