Abort incremental marking pulls in the requirement to also be able to abort on
the embedder side. In practice, aborting is never really needed and the GC
should just finalize the existing collection and do an atomic followup if exact
marking information is required.

Bug: chromium:843903
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: Ic471332d01b0c4be26b71a06248af03255c61a9d
Reviewed-on: https://chromium-review.googlesource.com/1225705Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55949}