Instread of using the transition array map to store the iteration index, we are using the constructor field of the map. Moreover, I removed the unchecked transition array accessors.

BUG=
R=mstarzinger@chromium.org, verwaest@chromium.org

Review URL: https://codereview.chromium.org/223533002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@20503 ce2b1a6d-e550-0410-aec6-3dcde31c8c00