If the input array is small, then the cost of a trip to the
runtime to transition the ElementsKind is too expensive.

Bug: 
Change-Id: Ib04f8567674a6f1f66f4c7263eba5fb4c58987aa
Reviewed-on: https://chromium-review.googlesource.com/544866
Commit-Queue: Michael Stanton <mvstanton@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46417}