If streaming compilation has been triggered on a worker, it can be
problematic to schedule a foreground task for the callback, since
workers might never return to the event queue. Hence, deliver the
callback in background. This is possible after this blink-side change:
https://crrev.com/c/1901592

R=ahaas@chromium.org
CC=​bbudge@chromium.org

Bug: chromium:1018029
Cq-Include-Trybots: luci.v8.try:v8_linux_blink_rel
Change-Id: I568c39cf97e94f6d1cec01090ece81e4521fa47c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1914199Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64946}