Fix compilation on 32-bit platforms after r19728

BUG=None
TBR=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/191043002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19729 ce2b1a6d-e550-0410-aec6-3dcde31c8c00