Map::MigrateToMap() now supports fast case (transition from a map that has run out of property space).

R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/347413002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21942 ce2b1a6d-e550-0410-aec6-3dcde31c8c00