Map::Normalize() introduced as single entry point for map normalization and Map::NotifyLeafMapLayoutChange() made private.

R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/263663002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21117 ce2b1a6d-e550-0410-aec6-3dcde31c8c00