Unify grow mode and stub kind

In the process, ensure that transition-causing element stores handle all cases of the transitioned receiver map.

Review URL: https://codereview.chromium.org/12390031

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13850 ce2b1a6d-e550-0410-aec6-3dcde31c8c00