This only available under --harmony-classes

BUG=v8:3571
LOG=Y
R=dslomov@chromium.org

Review URL: https://codereview.chromium.org/718473002

Cr-Commit-Position: refs/heads/master@{#25271}
git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25271 ce2b1a6d-e550-0410-aec6-3dcde31c8c00