BottomToolbarMediator implements SceneChangeObserver directly

This patch has the BottomToolbarMediator implement SceneChangeObserver
rather than making it an anonymous class. This change also allows us
to remove the observer when the mediator is destroyed.

Change-Id: I045058f434e8638bc6c114dff4d1f0ed85059714
Reviewed-on: https://chromium-review.googlesource.com/1136988
Commit-Queue: Matthew Jones <mdjones@chromium.org>
Reviewed-by: Pedro Amaral <amaralp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575738}
1 file changed