Keep dedicated layers for hiding animation

ui/views/corewm/window_animations.h

Index: ui/views/corewm/window_animations.h
diff --git a/ui/views/corewm/window_animations.h b/ui/views/corewm/window_animations.h
index f5728e6add64fc4ad60b8244540c8c6c28efec62..262eed16d006f55fbbe42c51eaf7736cdb3a2a62 100644
--- a/ui/views/corewm/window_animations.h
+++ b/ui/views/corewm/window_animations.h
@@ -88,6 +88,12 @@ VIEWS_EXPORT void SetWindowVisibilityAnimationVerticalPosition(
 VIEWS_EXPORT ui::ImplicitAnimationObserver* CreateHidingWindowAnimationObserver(
     aura::Window* window);
 
+// Detach the existing layer and recreate the new layer for the window
+// if there is a hiding animation in progress. This is used to keep the
+// hiding animation visible on top of active windows. Returns NULL if there
+// is no hiding animation in progress.
+VIEWS_EXPORT ui::Layer* DetachHidingAnimationLayer(aura::Window* window);
+
 // Returns false if the |window| didn't animate.
 VIEWS_EXPORT bool AnimateOnChildWindowVisibilityChanged(aura::Window* window,
                                                         bool visible);