quartz: Emulate root window as 1x1 bitmap

We subclass GdkWindowImplQuartz into a new GdkRootWindowImplQuartz,
and override the get_context method in order to do this cleanly.
Also made release_context a virtual method, since the root window has
to release its CGContextRef differently compared to normal windows.

gdk/quartz/gdkwindow-quartz.h

@@ -69,6 +69,33 @@ struct _GdkWindowImplQuartzClass
 
 GType _gdk_window_impl_quartz_get_type (void);
 
+
+/* Root window implementation for Quartz
+ */
+
+typedef struct _GdkRootWindowImplQuartz GdkRootWindowImplQuartz;
+typedef struct _GdkRootWindowImplQuartzClass GdkRootWindowImplQuartzClass;
+
+#define GDK_TYPE_ROOT_WINDOW_IMPL_QUARTZ              (_gdk_root_window_impl_quartz_get_type ())
+#define GDK_ROOT_WINDOW_IMPL_QUARTZ(object)           (G_TYPE_CHECK_INSTANCE_CAST ((object), GDK_TYPE_ROOT_WINDOW_IMPL_QUARTZ, GdkRootWindowImplQuartz))
+#define GDK_ROOT_WINDOW_IMPL_QUARTZ_CLASS(klass)      (G_TYPE_CHECK_CLASS_CAST ((klass), GDK_TYPE_ROOT_WINDOW_IMPL_QUARTZ, GdkRootWindowImplQuartzClass))
+#define GDK_IS_ROOT_WINDOW_IMPL_QUARTZ(object)        (G_TYPE_CHECK_INSTANCE_TYPE ((object), GDK_TYPE_ROOT_WINDOW_IMPL_QUARTZ))
+#define GDK_IS_ROOT_WINDOW_IMPL_QUARTZ_CLASS(klass)   (G_TYPE_CHECK_CLASS_TYPE ((klass), GDK_TYPE_ROOT_WINDOW_IMPL_QUARTZ))
+#define GDK_ROOT_WINDOW_IMPL_QUARTZ_GET_CLASS(obj)    (G_TYPE_INSTANCE_GET_CLASS ((obj), GDK_TYPE_ROOT_WINDOW_IMPL_QUARTZ, GdkRootWindowImplQuartzClass))
+
+struct _GdkRootWindowImplQuartz
+{
+  GdkWindowImplQuartz parent_instance;
+};
+ 
+struct _GdkRootWindowImplQuartzClass 
+{
+  GdkWindowImplQuartzClass parent_class;
+};
+
+GType _gdk_root_window_impl_quartz_get_type (void);
+
+
 G_END_DECLS
 
 #endif /* __GDK_WINDOW_QUARTZ_H__ */