We have HashMap for the strings. They got id sequentially. So we could use index sort.

BUG=none
R=alph@chromium.org, yangguo@chromium.org

Review URL: https://codereview.chromium.org/24174002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16734 ce2b1a6d-e550-0410-aec6-3dcde31c8c00