Use GSlice for GtkRequisition

Also add gtk_requisition_new to avoid memory allocator confusions when
using GtkRequisitions.

Based on a Christian Persch patch.
Fixes https://bugzilla.gnome.org/show_bug.cgi?id=461618

docs/reference/gtk/gtk3-sections.txt

@@ -4942,6 +4942,7 @@ gtk_widget_get_requisition
 gtk_widget_device_is_shadowed
 
 <SUBSECTION>
+gtk_requisition_new
 gtk_requisition_copy
 gtk_requisition_free
 

gtk/gtk.symbols

@@ -4312,6 +4312,7 @@ gtk_vseparator_new
 gtk_requisition_copy
 gtk_requisition_free
 gtk_requisition_get_type G_GNUC_CONST
+gtk_requisition_new G_GNUC_MALLOC
 gtk_widget_activate
 gtk_widget_is_composited
 gtk_widget_add_accelerator

gtk/gtkwidget.c

@@ -10240,6 +10240,22 @@ gtk_widget_class_path (GtkWidget *widget,
     }
 }
 
+/**
+ * gtk_requisition_new:
+ *
+ * Allocates a new #GtkRequisition structure and initializes its elements to zero.
+ *
+ * Returns: a new empty #GtkRequisition. The newly allocated #GtkRequisition should
+ *   be freed with gtk_requisition_free().
+ *
+ * Since: 3.0
+ */
+GtkRequisition *
+gtk_requisition_new (void)
+{
+  return g_slice_new0 (GtkRequisition);
+}
+
 /**
  * gtk_requisition_copy:
  * @requisition: a #GtkRequisition
@@ -10251,7 +10267,7 @@ gtk_widget_class_path (GtkWidget *widget,
 GtkRequisition *
 gtk_requisition_copy (const GtkRequisition *requisition)
 {
-  return (GtkRequisition *)g_memdup (requisition, sizeof (GtkRequisition));
+  return g_slice_dup (GtkRequisition, requisition);
 }
 
 /**
@@ -10263,7 +10279,7 @@ gtk_requisition_copy (const GtkRequisition *requisition)
 void
 gtk_requisition_free (GtkRequisition *requisition)
 {
-  g_free (requisition);
+  g_slice_free (GtkRequisition, requisition);
 }
 
 GType

gtk/gtkwidget.h

@@ -954,6 +954,7 @@ void       gtk_widget_set_has_tooltip       (GtkWidget   *widget,
 gboolean   gtk_widget_get_has_tooltip       (GtkWidget   *widget);
 
 GType           gtk_requisition_get_type (void) G_GNUC_CONST;
+GtkRequisition *gtk_requisition_new      (void) G_GNUC_MALLOC;
 GtkRequisition *gtk_requisition_copy     (const GtkRequisition *requisition);
 void            gtk_requisition_free     (GtkRequisition       *requisition);