Currently, young generation assumes that all the on-heap pointers are
compressed, which is currently not the case due to the backing-store
pointers in Blink. Fixing collections to have Member<> is not easy,
because the inlined collections may have the semantics that
 backing_pointer_ == inlined_buffer_;
where the inlined_buffer_ can be off-heap (e.g. on stack).

The CL introduces another type of barrier specifically for uncompressed
pointers. The followup is to use that barrier from Blink.

Bug: chromium:1029379
Change-Id: If0f519220658268dbdf915235c2e5afd7887dc0c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3695358Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81105}