This reduces chances of improper usage, see http://code.google.com/p/v8/issues/detail?id=586
for more details.

BUG=586

Review URL: http://codereview.chromium.org/555072

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3696 ce2b1a6d-e550-0410-aec6-3dcde31c8c00