Always wait for the main app window before starting a transition

When waiting for all the windows that belong to an activity, we
skipped the main window, in case it didn't had a surface yet. This
was a problem because with SurfaceViews: They set it's visibility
extremely early in the app visibility change cycle. Then, they use
another thread to draw content. Thus, they have drawn their first
frame pretty fast, where the main thread might still be in the
activity lifecycle phases. Then, we don't even have a surface for the
main window yet, but we start the app transition already because we
think the only interesting window for this app token is the
SurfaceView, which has already drawn.

Bug: 22207948
Change-Id: I708add3aab00575ae1707b25622b9b4614472892