Fix error message about read-only symbol properties.

R=rossberg@chromium.org
BUG=v8:3441
LOG=Y

Review URL: https://codereview.chromium.org/390783003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22377 ce2b1a6d-e550-0410-aec6-3dcde31c8c00