Better security checks when accessing named properties via Object.getOwnPropertyDescr...

Better security checks when accessing named properties via Object.getOwnPropertyDescriptor.

Current approach returns undefined descriptor if caller is not granted v8::HAS_ACCESS.
If the caller has v8::HAS_ACCESS, for no JS accessors regular v8::GET_ACCESS check is
performed and value property of the descriptor is set to undefined if caller doesn't
have proper access.  For JS accessors both v8::GET_ACCESS and v8::SET_ACCESS are checked
and affect if getter and setter would be stored in the descriptor.

Review URL: http://codereview.chromium.org/6286020

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6592 ce2b1a6d-e550-0410-aec6-3dcde31c8c00