Force pinned windows to always be scaleable.

Otherwise we have a race when switching it off at the end
of the animation when we don't move to fullscreen. Ensure
SCALE_TO_WINDOW is always enabled for windows while they
are in the pinned stack.

Bug: 27793381
Change-Id: Ia92465fd0d854f799caa8ed31edb4621af9fdecd
3 files changed