Reland "Remove remaining window states where window is shown with opacity 0. (https://codereview.ch…

ash/shelf/shelf_util.h

Index: ash/shelf/shelf_util.h
diff --git a/ash/shelf/shelf_util.h b/ash/shelf/shelf_util.h
index f4c4b80e5d8f62e1b5b7c9ce16e716b3cbd20a96..7e5dae17ab7363946b14344af2621001e97c7954 100644
--- a/ash/shelf/shelf_util.h
+++ b/ash/shelf/shelf_util.h
@@ -15,6 +15,11 @@ class Window;
 
 namespace ash {
 
+// A property key to store the id of the ShelfItem associated with the window.
+extern const aura::WindowProperty<ShelfID>* const kShelfID;
+
+// A property key to store the resource id and title of the item shown on the
+// shelf for this window.
 extern const aura::WindowProperty<ShelfItemDetails*>* const
     kShelfItemDetailsKey;