Also only transition and/or change anything to the backing store if we are
actually going to delete anything.

BUG=

Review URL: https://chromiumcodereview.appspot.com/11358011

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12840 ce2b1a6d-e550-0410-aec6-3dcde31c8c00