Process global accessors for total physical size and used size are
needed for blink. These are implemented via an allocation observer that
atomically updates static counters.

The public api only provides getters for the counters. An internal class
is in charge of updating the counters as needed. A similar split is also
applied to IsAnyIncrementalOrConcurrentMarking().

Drive-by: ProcessHeap is merged into cppgc::internal::WriteBarrier.

Bug: chromium:1056170
Change-Id: Iaedebd1ac9d49238ce6bdd52ffa5d1ef4d28203d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2695394
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72832}

Adds a cross-thread reference for strongly and weakly retaining
objects on a thread other than the thread that owns the object.

The intended use of the reference is by setting it up on the
originating thread, holding the object alive from another thread, and
ultimately accessing the object again on the originating thread.

The reference has known caveats:
- It's unsafe to use when the heap may terminate;
- It's unsafe to transitively reach through the graph because of
  compaction;

Change-Id: I84fbdde69a099eb54af5b93c34e2169915b17e64
Bug: chromium:1056170
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2436449
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70428}

This moves from Blink:
1) implementation of the marking write barrier;
2) WriteBarrierWorklist to Marker;
3) incremental/concurrent marking options.

Bug: chromium:1056170
Change-Id: Ia3e31ffd920a99803420b1453695fe2fb8d843b8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2218064
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68108}

Please take a look at tools/v8windbg/README.md for an overview of what
v8windbg can do and how it's structured. This platform-specific
debugging plugin makes use of the data provided by the V8 postmortem
debugging API in tools/debug_helper.

Note: This code began as https://github.com/billti/v8dbg and then moved
into the Edge repository, where I added features gradually and got code
reviews for individual changes. Now, taken in its entirety, it's an
obnoxiously large CL. I'm open to breaking it up into a few chunks if
that would be preferable.

Bug: v8:9376
Change-Id: I3e503de00bb1aea870ae83e9bd99e4e2eab9ef98
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2031700Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Reviewed-by: Tamer Tas <tmrts@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#66319}