for reasons that are not obvious.  Now we make objects into fast-case objects
when they are made prototypes for other objects, but we do not mark objects
that are already fast case with a bit that helps keep them in fast case.
Review URL: https://chromiumcodereview.appspot.com/10556004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11831 ce2b1a6d-e550-0410-aec6-3dcde31c8c00