session-bin: add _get_n_children() method

lib/wp/session-bin.c

@@ -117,6 +117,18 @@ wp_session_bin_remove (WpSessionBin *self, WpSessionItem *item)
   return g_ptr_array_remove_fast (priv->items, item);
 }
 
+/**
+ * wp_session_bin_get_n_children:
+ * @self: the session bin
+ *
+ * Returns: the number of child items in the bin
+ */
+guint
+wp_session_bin_get_n_children (WpSessionBin *self)
+{
+  WpSessionBinPrivate *priv = wp_session_bin_get_instance_private (self);
+  return priv->items->len;
+}
 
 struct _WpSessionBinIterator
 {

lib/wp/session-bin.h

@@ -42,6 +42,9 @@ gboolean wp_session_bin_add (WpSessionBin *self, WpSessionItem *item);
 WP_API
 gboolean wp_session_bin_remove (WpSessionBin *self, WpSessionItem *item);
 
+WP_API
+guint wp_session_bin_get_n_children (WpSessionBin *self);
+
 WP_API
 WpIterator *wp_session_bin_iterate (WpSessionBin *self);