The CL provides a way for the embedder to hook in a special malloc-like
allocator that will be used for zone allocations.

An alternative approach would be to use weak functions with branches,
checking whether the functions were available at link-time. Those
branches could be optimized away with LTOs, so they would essentially
be free. However, the weak function approach is not portable (e.g.
there is no easy way to emulate it with msvc). The approach can be
revisited if indirect call turns out to be expensive (e.g. on hardware
with weak branch target predictors).

The CL is a prerequisite for running PCScan in the renderer process.

Bug: chromium:1249550
Change-Id: I221dcb2486c13e8e6e6761839ba391978319bde4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3172760Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77012}