We don't necessarily want a big refactor here, but much of the UI is only shown on Android or only shown on Windows.  Very little is shown on both (though Linux may show both for testing purposes).

There are several ways we could make it clear what is Android-only and what is Windows-only.  For example, we could split ui_scene_creator into ui_scene_creator_win.h, ui_scene_creator_android.h.