Keyed store stub sits high in sorting profiles.

Swapping allows to save us additional type checks as we could both read and
write elmenets (on fast path) without them.

Review URL: http://codereview.chromium.org/1709008

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4551 ce2b1a6d-e550-0410-aec6-3dcde31c8c00