In the case where the array is a fast packed array, the CSA no longer needs
to check whether the prototype has elements. This only needed when the array
is holey.

This is a follow-up of CL #1183671.

Change-Id: I0087b827200995c741141f3183bf9a2c748d3b55
Reviewed-on: https://chromium-review.googlesource.com/1188315Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Commit-Queue: Hai Dang <dhai@google.com>
Cr-Commit-Position: refs/heads/master@{#55409}