AST ids only need to be unique, so there is no need to fiddle around with them.

R=dslomov@chromium.org

Review URL: https://codereview.chromium.org/633053002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24433 ce2b1a6d-e550-0410-aec6-3dcde31c8c00