Fix build.

GCC needs definitions for constant members (clang doesn't).

TBR=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/511133002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23480 ce2b1a6d-e550-0410-aec6-3dcde31c8c00