A LocalHeap creates and owns an instance of MarkingBarrier. A pointer to
the marking barrier is set to a thread_local variable for a quick access.

WriteBarrier::MarkingSlow fetches the thread_local variable and invokes
the write barrier if it is set. Otherwise, it invokes the main thread
heap()->marking_barrier().

Each marking barrier has its own local marking worklist that is
published during scavenge (for updating pointers) and at finalization
of incremental marking.

Typed-slot recording does not work yet because it is not thread-safe.
It will be fixed in a subsequent CL.

Bug: v8:10315
Change-Id: I221a906436cd91e7405a253ce0eb06cf68046f2c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2354809
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69448}