Add default GtkLayoutManagerClass.get_request_mode()

Just like GtkContainer provides a default implementation of
GtkWidgetClass.get_request_mode(), we can do the same inside
GtkLayoutManager.

A default implementation preserves the behavior of existing widgets that
moved, or will move, to a GtkLayoutManager.

gtk/gtkboxlayout.c

@@ -199,42 +199,6 @@ get_spacing (GtkBoxLayout *self,
   return css_spacing + self->spacing;
 }
 
-static GtkSizeRequestMode
-gtk_box_layout_get_request_mode (GtkLayoutManager *layout_manager,
-                                 GtkWidget        *widget)
-{
-  GtkWidget *child;
-  int wfh = 0, hfw = 0;
-
-  for (child = _gtk_widget_get_first_child (widget);
-       child != NULL;
-       child = _gtk_widget_get_next_sibling (child))
-    {
-      GtkSizeRequestMode mode = gtk_widget_get_request_mode (child);
-
-      switch (mode)
-        {
-        case GTK_SIZE_REQUEST_HEIGHT_FOR_WIDTH:
-          hfw += 1;
-          break;
-
-        case GTK_SIZE_REQUEST_WIDTH_FOR_HEIGHT:
-          wfh += 1;
-          break;
-
-        case GTK_SIZE_REQUEST_CONSTANT_SIZE:
-        default:
-          break;
-        }
-    }
-
-  if (hfw == 0 && wfh == 0)
-    return GTK_SIZE_REQUEST_CONSTANT_SIZE;
-  else
-    return wfh > hfw ? GTK_SIZE_REQUEST_WIDTH_FOR_HEIGHT
-                     : GTK_SIZE_REQUEST_HEIGHT_FOR_WIDTH;
-}
-
 static void
 gtk_box_layout_compute_size (GtkBoxLayout *self,
                              GtkWidget    *widget,
@@ -738,7 +702,6 @@ gtk_box_layout_class_init (GtkBoxLayoutClass *klass)
   gobject_class->set_property = gtk_box_layout_set_property;
   gobject_class->get_property = gtk_box_layout_get_property;
 
-  layout_manager_class->get_request_mode = gtk_box_layout_get_request_mode;
   layout_manager_class->measure = gtk_box_layout_measure;
   layout_manager_class->allocate = gtk_box_layout_allocate;
 

gtk/gtkcustomlayout.c

@@ -36,7 +36,7 @@ gtk_custom_layout_get_request_mode (GtkLayoutManager *manager,
   if (self->request_mode_func != NULL)
     return self->request_mode_func (widget);
 
-  return GTK_SIZE_REQUEST_CONSTANT_SIZE;
+  return GTK_LAYOUT_MANAGER_CLASS (gtk_custom_layout_parent_class)->get_request_mode (manager, widget);
 }
 
 static void

gtk/gtkfixedlayout.c

@@ -208,6 +208,13 @@ gtk_fixed_layout_child_get_position (GtkFixedLayoutChild *child)
 
 G_DEFINE_TYPE (GtkFixedLayout, gtk_fixed_layout, GTK_TYPE_LAYOUT_MANAGER)
 
+static GtkSizeRequestMode
+gtk_fixed_layout_get_request_mode (GtkLayoutManager *layout_manager,
+                                   GtkWidget        *widget)
+{
+  return GTK_SIZE_REQUEST_CONSTANT_SIZE;
+}
+
 static void
 gtk_fixed_layout_measure (GtkLayoutManager *layout_manager,
                           GtkWidget        *widget,
@@ -316,6 +323,7 @@ gtk_fixed_layout_class_init (GtkFixedLayoutClass *klass)
 
   layout_class->layout_child_type = GTK_TYPE_FIXED_LAYOUT_CHILD;
 
+  layout_class->get_request_mode = gtk_fixed_layout_get_request_mode;
   layout_class->measure = gtk_fixed_layout_measure;
   layout_class->allocate = gtk_fixed_layout_allocate;
   layout_class->create_layout_child = gtk_fixed_layout_create_layout_child;

gtk/gtklayoutmanager.c

@@ -75,7 +75,7 @@
 
 #include "gtklayoutmanagerprivate.h"
 #include "gtklayoutchild.h"
-#include "gtkwidget.h"
+#include "gtkwidgetprivate.h"
 
 #ifdef G_ENABLE_DEBUG
 #define LAYOUT_MANAGER_WARN_NOT_IMPLEMENTED(m,method)   G_STMT_START {  \
@@ -101,7 +101,36 @@ static GtkSizeRequestMode
 gtk_layout_manager_real_get_request_mode (GtkLayoutManager *manager,
                                           GtkWidget        *widget)
 {
-  return GTK_SIZE_REQUEST_CONSTANT_SIZE;
+  int hfw = 0, wfh = 0;
+  GtkWidget *child;
+
+  for (child = _gtk_widget_get_first_child (widget);
+       child != NULL;
+       child = _gtk_widget_get_next_sibling (child))
+    {
+      GtkSizeRequestMode res = gtk_widget_get_request_mode (child);
+
+      switch (res)
+        {
+        case GTK_SIZE_REQUEST_HEIGHT_FOR_WIDTH:
+          hfw += 1;
+          break;
+
+        case GTK_SIZE_REQUEST_WIDTH_FOR_HEIGHT:
+          wfh += 1;
+          break;
+
+        case GTK_SIZE_REQUEST_CONSTANT_SIZE:
+        default:
+          break;
+        }
+    }
+
+ if (hfw == 0 && wfh == 0)
+   return GTK_SIZE_REQUEST_CONSTANT_SIZE;
+
+ return hfw > wfh ? GTK_SIZE_REQUEST_HEIGHT_FOR_WIDTH
+                  : GTK_SIZE_REQUEST_WIDTH_FOR_HEIGHT;
 }
 
 static void