Enable logging script events and code position events during a
background compile. This isn't technically thread-safe, but neither
are the existing logger accesses in the parser, so something has to
be done here in general.

Bug: chromium:1011762
Change-Id: I3b610c3bb146880ef826928b6f341f402ca6247e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2162853Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69426}