Reland of r20606: Further ElementsAccessor handlification (GetKeyForIndex(), GetCapacity(), GetType() and GetAttributes()).
It was not related to test failures.

R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/230373007

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@20616 ce2b1a6d-e550-0410-aec6-3dcde31c8c00