[goffice] Make css theming work again with gtk+-3.20.

[Jean Bréfort <jbrefort src gnome org>]

commit a854534ddcb40edaae7aecd2a0ff4e4528bac468
Author: Jean Brefort <jean brefort normalesup org>
Date:   Fri Apr 29 13:51:16 2016 +0200

    Make css theming work again with gtk+-3.20.

 ChangeLog                 |    5 +++++
 goffice/canvas/goc-item.c |    3 +++
 2 files changed, 8 insertions(+), 0 deletions(-)
---
diff --git a/ChangeLog b/ChangeLog
index b76a069..84d8fbe 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2016-04-29  Jean Brefort  <jean brefort normalesup org>
+
+       * goffice/canvas/goc-item.c (cb_hierarchy_changed): make css work again with
+       gtk+-3.20.
+
 2016-04-24  Jean Brefort  <jean brefort normalesup org>
 
        * goffice/graph/gog-axis.c (gog_axis_view_size_allocate): fix an infinite
diff --git a/goffice/canvas/goc-item.c b/goffice/canvas/goc-item.c
index 3e2aa2c..9a139bc 100644
--- a/goffice/canvas/goc-item.c
+++ b/goffice/canvas/goc-item.c
@@ -870,6 +870,9 @@ cb_hierarchy_changed (const GocItem *item)
                path = gtk_widget_path_new ();
 
        gtk_widget_path_append_type (path, G_TYPE_FROM_INSTANCE (item));
+#if GTK_CHECK_VERSION(3,20,0)
+       gtk_widget_path_iter_set_object_name (path, -1, G_OBJECT_TYPE_NAME (item));
+#endif
        gtk_style_context_set_path (context, path);
        gtk_widget_path_free (path);
        gtk_style_context_set_parent (context, pcontext);