Enable automatic FAB show/hide to work without minHeight

Currently, the automatic showing/hiding of the FAB does
not work if a minHeight is not set on the ABL or it's last
child. As a fallback, we now hide if 1/3 on the ABL is
visible.

Change-Id: Id05fbf4ade3572fc5adda9ebb0812f311ceb730b
1 file changed