Reland "Fix stepping in for-loops."

BUG=v8:3634
LOG=N
R=ulan@chromium.org

Review URL: https://codereview.chromium.org/688243005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25279 ce2b1a6d-e550-0410-aec6-3dcde31c8c00