Since we never need to ask it of a MaybeObject, put it with the other
oddball testers in class Object for consistency.

Review URL: http://codereview.chromium.org/6138004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6216 ce2b1a6d-e550-0410-aec6-3dcde31c8c00