[gnome-builder] layout: avoid jumps in natural size

[Christian Hergert <chergert src gnome org>]

commit 552b63046e5023f688d9e37e4c0972f11a25e6b4
Author: Christian Hergert <chergert redhat com>
Date:   Tue Mar 13 16:50:07 2018 -0700

    layout: avoid jumps in natural size
    
    This helps reduce size jitter in the grid due to changes of natural
    size in the stack header (such as from our "modified asterisk").

 src/libide/layout/ide-layout-stack-header.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)
---
diff --git a/src/libide/layout/ide-layout-stack-header.c b/src/libide/layout/ide-layout-stack-header.c
index 782cfd094..faa754511 100644
--- a/src/libide/layout/ide-layout-stack-header.c
+++ b/src/libide/layout/ide-layout-stack-header.c
@@ -470,6 +470,25 @@ ide_layout_stack_header_add (GtkContainer *container,
   update_widget_providers (widget, self);
 }
 
+static void
+ide_layout_stack_header_get_preferred_width (GtkWidget *widget,
+                                             gint      *min_width,
+                                             gint      *nat_width)
+{
+  g_assert (IDE_IS_LAYOUT_STACK_HEADER (widget));
+  g_assert (min_width != NULL);
+  g_assert (nat_width != NULL);
+
+  GTK_WIDGET_CLASS (ide_layout_stack_header_parent_class)->get_preferred_width (widget, min_width, 
nat_width);
+
+  /*
+   * We don't want changes to the natural width to influence our positioning of
+   * the grid separators (unless necessary). So instead, we always return our
+   * minimum position as our natural size and let the grid expand as necessary.
+   */
+  *nat_width = *min_width;
+}
+
 static void
 ide_layout_stack_header_destroy (GtkWidget *widget)
 {
@@ -561,6 +580,7 @@ ide_layout_stack_header_class_init (IdeLayoutStackHeaderClass *klass)
   object_class->set_property = ide_layout_stack_header_set_property;
 
   widget_class->destroy = ide_layout_stack_header_destroy;
+  widget_class->get_preferred_width = ide_layout_stack_header_get_preferred_width;
 
   container_class->add = ide_layout_stack_header_add;