The PropertyArray may store the hash of it's parent object. This hash
can be installed at various points. Meanwhile, the background compiler
thread inspects the length field.

BUG=chromium:1220974

Change-Id: I7b13fd4546fb48e649fcbf67dee02d7c668393f2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2967471
Commit-Queue: Michael Stanton <mvstanton@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75208}