[mutter] window: Add get_default_layer() helper

[Jonas Ådahl <jadahl src gnome org>]

commit b753213f9b86659f800729416f3572d046678c8b
Author: Florian Müllner <fmuellner gnome org>
Date:   Tue Nov 26 21:01:37 2019 +0100

    window: Add get_default_layer() helper
    
    Most of the layer computation that the stack does actually depends
    on the windowing backend, so we will move it to a vfunc.
    
    However before we do that, split out the bit that will be shared.
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/949

 src/core/stack.c          |  7 +------
 src/core/window-private.h |  1 +
 src/core/window.c         | 11 +++++++++++
 3 files changed, 13 insertions(+), 6 deletions(-)
---
diff --git a/src/core/stack.c b/src/core/stack.c
index 7a9669020..f97909a58 100644
--- a/src/core/stack.c
+++ b/src/core/stack.c
@@ -480,12 +480,7 @@ get_standalone_layer (MetaWindow *window)
         }
       break;
     default:
-      if (window->wm_state_below)
-        layer = META_LAYER_BOTTOM;
-      else if (window->wm_state_above && !META_WINDOW_MAXIMIZED (window))
-        layer = META_LAYER_TOP;
-      else
-        layer = META_LAYER_NORMAL;
+      layer = meta_window_get_default_layer (window);
       break;
     }
 
diff --git a/src/core/window-private.h b/src/core/window-private.h
index 8b853b3cb..3fd9f146e 100644
--- a/src/core/window-private.h
+++ b/src/core/window-private.h
@@ -737,6 +737,7 @@ void meta_window_update_keyboard_resize (MetaWindow *window,
                                          gboolean    update_cursor);
 void meta_window_update_keyboard_move   (MetaWindow *window);
 
+MetaStackLayer meta_window_get_default_layer (MetaWindow *window);
 void meta_window_update_layer (MetaWindow *window);
 
 void meta_window_recalc_features    (MetaWindow *window);
diff --git a/src/core/window.c b/src/core/window.c
index 75f62fb24..45c9c6ca6 100644
--- a/src/core/window.c
+++ b/src/core/window.c
@@ -6946,6 +6946,17 @@ meta_window_update_keyboard_move (MetaWindow *window)
                      &x, &y);
 }
 
+MetaStackLayer
+meta_window_get_default_layer (MetaWindow *window)
+{
+  if (window->wm_state_below)
+    return META_LAYER_BOTTOM;
+  else if (window->wm_state_above && !META_WINDOW_MAXIMIZED (window))
+    return META_LAYER_TOP;
+  else
+    return META_LAYER_NORMAL;
+}
+
 void
 meta_window_update_layer (MetaWindow *window)
 {