Fix debug compilation after r18337

BUG=chromium:327298
LOG=N
TBR=hpayer@chromium.org

Review URL: https://codereview.chromium.org/115113009

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18339 ce2b1a6d-e550-0410-aec6-3dcde31c8c00