In the ElementsAccessor fast-path for Array.prototype.includes, we
iterate backing-store elements according to start and length numbers
which might or might not be within the JSArray::length field, for
example when side-effects changed the receiver while start and length
are computed. So even when we have a packed ElementsKind, we might still
observe the hole. This is fine, since logical out-of-bounds accesses
are safe in this case, but it means we must not rely on the
ElementsKind telling us if we can encounter holes.

Bug: chromium:897098
Change-Id: I17db38246aef6edbdd5cee30598cbf7619aba6d8
Reviewed-on: https://chromium-review.googlesource.com/c/1293571Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56884}