To avoid a performance regression for context creation with snapshots, we avoid
creating a useless long map chain for regular expressions, keeping the snapshot
size almost the same as before.

Review URL: https://chromiumcodereview.appspot.com/10440045

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11664 ce2b1a6d-e550-0410-aec6-3dcde31c8c00