ES6: Add support for Array.prototype.fill()

BUG=v8:3273
LOG=Y
R=dslomov@chromium.org

Review URL: https://codereview.chromium.org/240873002

Patch from Adrian Perez <aperez@igalia.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21074 ce2b1a6d-e550-0410-aec6-3dcde31c8c00