[gimp/gtk3-port] app: add missing const to gimp_cell_renderer_button_activate()

[Michael Natterer <mitch src gnome org>]

commit f5d5440a3c20a5d238675e44398348e54962cec3
Author: Michael Natterer <mitch gimp org>
Date:   Mon Apr 30 18:21:42 2018 +0200

    app: add missing const to gimp_cell_renderer_button_activate()

 app/widgets/gimpcellrendererbutton.c |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)
---
diff --git a/app/widgets/gimpcellrendererbutton.c b/app/widgets/gimpcellrendererbutton.c
index 93f52c9..3bc2716 100644
--- a/app/widgets/gimpcellrendererbutton.c
+++ b/app/widgets/gimpcellrendererbutton.c
@@ -40,8 +40,8 @@ static gboolean gimp_cell_renderer_button_activate (GtkCellRenderer     *cell,
                                                     GdkEvent            *event,
                                                     GtkWidget           *widget,
                                                     const gchar         *path,
-                                                    GdkRectangle        *background_area,
-                                                    GdkRectangle        *cell_area,
+                                                    const GdkRectangle  *background_area,
+                                                    const GdkRectangle  *cell_area,
                                                     GtkCellRendererState flags);
 
 
@@ -99,8 +99,8 @@ gimp_cell_renderer_button_activate (GtkCellRenderer      *cell,
                                     GdkEvent             *event,
                                     GtkWidget            *widget,
                                     const gchar          *path,
-                                    GdkRectangle         *background_area,
-                                    GdkRectangle         *cell_area,
+                                    const GdkRectangle   *background_area,
+                                    const GdkRectangle   *cell_area,
                                     GtkCellRendererState  flags)
 {
   GimpCellRendererButton *cell_button = GIMP_CELL_RENDERER_BUTTON (cell);