First step to cleanup the power-of-2 mess.

TEST=base-unittests,cctest,mjsunit
R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/528993002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23617 ce2b1a6d-e550-0410-aec6-3dcde31c8c00