[gtk/wip/chergert/quartz4u] macos: add missing declaration

[Christian Hergert <chergert src gnome org>]

commit be728e4c4e4f8bd94f84cf076a89c271476261fd
Author: Christian Hergert <chergert redhat com>
Date:   Mon May 4 15:24:49 2020 -0700

    macos: add missing declaration

 gdk/macos/gdkmacossurface-private.h | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/gdk/macos/gdkmacossurface-private.h b/gdk/macos/gdkmacossurface-private.h
index 2eea9b07cd..6ea572b9da 100644
--- a/gdk/macos/gdkmacossurface-private.h
+++ b/gdk/macos/gdkmacossurface-private.h
@@ -78,6 +78,8 @@ void               _gdk_macos_surface_update_position         (GdkMacosSurface
 void               _gdk_macos_surface_damage_cairo            (GdkMacosSurface    *self,
                                                                cairo_surface_t    *surface,
                                                                cairo_region_t     *painted);
+void               _gdk_macos_surface_set_is_key              (GdkMacosSurface    *self,
+                                                               gboolean            is_key);
 
 G_END_DECLS