Since RO_SPACE objects can't move then IsDereferenceAllowed, just return
true for any objects in RO_SPACE.

R=leszeks

Bug: v8:7786
Change-Id: I67d2d8902a3c2196991bf57ba719c8b05220cdbb
Reviewed-on: https://chromium-review.googlesource.com/1138324Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54472}