Add media_log when block model ends up being used.

This makes it easier to tell when it's being used during debugging
on release devices.

R=eugene

Bug: 327625558
Change-Id: Idf2e53a55666eab8f9ae5cb31ccdd2399c502dd7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6219707
Reviewed-by: Eugene Zemtsov <eugene@chromium.org>
Auto-Submit: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Eugene Zemtsov <eugene@chromium.org>
Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1413749}