Add a path into embedder tracing on allocation. This is safe as as Blink
is not allowed to call into V8 during object construction.

This is a reland of caed2cc0.

Also relands the cleanups of ce02d86b.

Bug: chromium:843903
Change-Id: Ic89792fe68337c540a1a93629aee2e92b8774ab2
Reviewed-on: https://chromium-review.googlesource.com/c/1350992Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57847}