[MetaWindow] Accessor for the instance part of WM_CLASS property

https://bugzilla.gnome.org/show_bug.cgi?id=613128

src/core/window.c

@@ -8924,7 +8924,7 @@ meta_window_get_description (MetaWindow *window)
  * meta_window_get_wm_class:
  * @window: a #MetaWindow
  *
- * Return the current value of the WM_CLASS X property.
+ * Return the current value of the name part of WM_CLASS X property.
  */
 const char *
 meta_window_get_wm_class (MetaWindow *window)
@@ -8935,6 +8935,21 @@ meta_window_get_wm_class (MetaWindow *window)
   return window->res_class;
 }
 
+/**
+ * meta_window_get_wm_class_instance:
+ * @window: a #MetaWindow
+ *
+ * Return the current value of the instance part of WM_CLASS X property.
+ */
+const char *
+meta_window_get_wm_class_instance (MetaWindow *window)
+{
+  if (!window)
+    return NULL;
+
+  return window->res_name;
+}
+
 /**
  * meta_window_get_compositor_private:
  * @window: a #MetaWindow

src/include/window.h

@@ -88,6 +88,7 @@ void     meta_window_activate_with_workspace (MetaWindow    *window,
                                               MetaWorkspace *workspace);
 const char * meta_window_get_description (MetaWindow *window);
 const char * meta_window_get_wm_class (MetaWindow *window);
+const char * meta_window_get_wm_class_instance (MetaWindow *window);
 /* Return whether the window would be showing if we were on its workspace */
 gboolean    meta_window_showing_on_its_workspace (MetaWindow *window);