[Media Controller] Fix dcheck with image observer

The mojo::MediaSession instance is owned by
AudioFocusRequest. Therefore, we need to wrap callbacks
to get the image bitmap so they are owned by that class.

BUG=985874

Change-Id: I3f11cbc76df67bf84f0dd22748a576ec6c7bac2c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1709800
Reviewed-by: Tommy Steimel <steimel@chromium.org>
Commit-Queue: Becca Hughes <beccahughes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#679603}
3 files changed