[gtk/wip/baedert/gl-rework] cssimage: Skip is_computed images

[Timm Bäder <baedert src gnome org>]

commit 1a010b2c325326c15a1f9be46ff42d62f1657731
Author: Timm Bäder <mail baedert org>
Date:   Mon Jan 20 10:35:21 2020 +0100

    cssimage: Skip is_computed images
    
    Not sure if this isn't potentially slower, but alas.

 gtk/gtkcssimage.c | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/gtk/gtkcssimage.c b/gtk/gtkcssimage.c
index 4b9c781d80..3179031f9a 100644
--- a/gtk/gtkcssimage.c
+++ b/gtk/gtkcssimage.c
@@ -184,6 +184,9 @@ _gtk_css_image_compute (GtkCssImage      *image,
   gtk_internal_return_val_if_fail (GTK_IS_CSS_STYLE (style), NULL);
   gtk_internal_return_val_if_fail (parent_style == NULL || GTK_IS_CSS_STYLE (parent_style), NULL);
 
+  if (gtk_css_image_is_computed (image))
+    return g_object_ref (image);
+
   klass = GTK_CSS_IMAGE_GET_CLASS (image);
 
   return klass->compute (image, property_id, provider, style, parent_style);