[libdazzle] tree: add padding to tree

[Christian Hergert <chergert src gnome org>]

commit 87c25cedcd107f9c992fa3b6509c9640d5f989c2
Author: Christian Hergert <chergert redhat com>
Date:   Sat Dec 2 15:05:58 2017 -0800

    tree: add padding to tree
    
    We need to break ABI on the tree this cycle, so let's just ensure we have
    padding so we don't have to do it again in the future.

 src/tree/dzl-tree.h |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/src/tree/dzl-tree.h b/src/tree/dzl-tree.h
index a29d71b..07da343 100644
--- a/src/tree/dzl-tree.h
+++ b/src/tree/dzl-tree.h
@@ -63,6 +63,9 @@ struct _DzlTreeClass
                           const gchar *param);
   void (*populate_popup) (DzlTree     *self,
                           GtkWidget   *widget);
+
+  /*< private >*/
+  gpointer _padding[12];
 };
 
 DZL_AVAILABLE_IN_ALL