Only generate a single normal IC per kind per slow-mode map.

BUG=
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/429543004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22680 ce2b1a6d-e550-0410-aec6-3dcde31c8c00