A Phi is necessary to carry the ElementsKind forward in case transitions
are taken.

Bug: chromium:747075
Change-Id: I9d9d66b0219fe3f67d08536f4d478ee300c76acb
Reviewed-on: https://chromium-review.googlesource.com/583090Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Michael Stanton <mvstanton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46852}