Our own ARRAY_SIZE() was pretty bad at error checking. If you use
arrasize() in a wrong way, the compiler will issue an error instead of
silently doing the wrong thing. The previous ARRAY_SIZE() macro is still
available as ARRAYSIZE_UNSAFE() similar to Chrome.

R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/501323002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23389 ce2b1a6d-e550-0410-aec6-3dcde31c8c00