This Cl changes the priority of baseline compilation from kUserVisible
to kUserBlocking. Once baseline compilation finishes, the priority is
reduced to kUserVisible. The reason for using kUserBlocking is that
thereby TurboFan compilation cannot block Liftoff compilation anymore.
Additionally, kUserBlocking is quite appropriate, as the initial
compilation does block a whole section of a web app from execution.

R=clemensb@chromium.org

Bug: v8:11088
Change-Id: Ifde42d20f36d4c0a5122b0008311ccdffbb60e48
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2519559
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71404}