gdk: Make GdkWindowImpl inherit from GObject

gdk/gdkwindowimpl.c

@@ -31,7 +31,7 @@
 #include "gdkinternals.h"
 
 
-G_DEFINE_TYPE (GdkWindowImpl, gdk_window_impl, GDK_TYPE_DRAWABLE);
+G_DEFINE_TYPE (GdkWindowImpl, gdk_window_impl, G_TYPE_OBJECT);
 
 
 static void

gdk/gdkwindowimpl.h

@@ -43,12 +43,12 @@ typedef struct _GdkWindowImplClass  GdkWindowImplClass;
 
 struct _GdkWindowImpl
 {
-  GdkDrawable  parent;
+  GObject parent;
 };
 
 struct _GdkWindowImplClass
 {
-  GdkDrawableClass parent_class;
+  GObjectClass parent_class;
 
   cairo_surface_t *
                (* ref_cairo_surface)    (GdkWindow       *window);