If the elements fixed array is large enough, it must be allocated in
large-object space. This fixes two cases in which we'd incorrectly
assume elements fits into new space.

There are potentially quite a few other spots affected by a similar
issue, and we should find a more robust solution. See also:
crbug.com/636391.

Bug: v8:6716
Change-Id: I91f09355ac6b7cf399e13cc21d34113a506e58fb
Reviewed-on: https://chromium-review.googlesource.com/623808Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47495}