HasNonSmiUse should ignore tagged uses

R=verwaest@chromium.org

Review URL: https://chromiumcodereview.appspot.com/21105006

Patch from Weiliang Lin <weiliang.lin2@gmail.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15950 ce2b1a6d-e550-0410-aec6-3dcde31c8c00