This reverts commit bdc89ae76c15f3ef2626f8849744500248aec3ba.

This is a revert of the revert with test/webkit updated as needed.

Original CL Description:

http://people.mozilla.org/~jorendorff/es6-draft.html#sec-object.setprototypeof

This just exposes the internal %SetPrototype and adds all the required
type checks as specified.

BUG=v8:2675
LOG=Y
R=dslomov@chromium.org, rossberg@chromium.org

Review URL: https://codereview.chromium.org/144193005

Patch from Erik Arvidsson <arv@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@18739 ce2b1a6d-e550-0410-aec6-3dcde31c8c00