Also, have the stub cache set a valid MajorKey on stubs it creates.
Getting weird random bits frightens and confuses the poor simple type feedback oracle.

R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/108443004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@18309 ce2b1a6d-e550-0410-aec6-3dcde31c8c00