The FastNewContextStub always allocates in new space, so we don't
need to update the write barrier when copying the parameters to
the newly allocated context.

R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/297203002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21481 ce2b1a6d-e550-0410-aec6-3dcde31c8c00