It is possible that the foreground task is unable to clear the
scheduled unfinished work, eventually leading to an OOM.

We use either code_range on 64 bit, or the capacity of the code space,
as a heuristic for how much memory to use for compilation.

The change avoids blocking the background threads while we're over
the memory threshold. This is to avoid starving the GC.

Bug: v8:6492, chromium:732010
Change-Id: Ic2647d9fa71af4f8cdd2149a434b107cbed3a6c3
Reviewed-on: https://chromium-review.googlesource.com/540763
Commit-Queue: Mircea Trofin <mtrofin@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46029}