[gnome-builder] GbDocumentManager: add helper to get singleton instance.

[Christian Hergert <chergert src gnome org>]

commit 66b4d02a936bc7be2ae688b15fe015bf81f89ac9
Author: Christian Hergert <christian hergert me>
Date:   Tue Dec 2 18:38:06 2014 -0800

    GbDocumentManager: add helper to get singleton instance.

 src/documents/gb-document-manager.c |   18 ++++++++++++++++++
 1 files changed, 18 insertions(+), 0 deletions(-)
---
diff --git a/src/documents/gb-document-manager.c b/src/documents/gb-document-manager.c
index 118865e..9f27042 100644
--- a/src/documents/gb-document-manager.c
+++ b/src/documents/gb-document-manager.c
@@ -34,6 +34,24 @@ gb_document_manager_new (void)
 }
 
 /**
+ * gb_document_manager_get_default:
+ *
+ * Retrieves the singleton instance of #GbDocumentManager.
+ *
+ * Returns: (transfer none): A #GbDocumentManager.
+ */
+GbDocumentManager *
+gb_document_manager_get_default (void)
+{
+  static GbDocumentManager *instance;
+
+  if (!instance)
+    instance = gb_document_manager_new ();
+
+  return instance;
+}
+
+/**
  * gb_document_manager_find_by_file:
  * @manager: A #GbDocumentManager.
  * @file: A #GFile.