Directly create API functions with readonly prototypes rather than converting. Remove FunctionSetReadOnlyPrototype.

BUG=
R=ishell@chromium.org

Review URL: https://codereview.chromium.org/274463003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21243 ce2b1a6d-e550-0410-aec6-3dcde31c8c00