diff -r 000000000000 -r 6474c204b198 widget/gtk/nsGtkUtils.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/widget/gtk/nsGtkUtils.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,24 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* vim:expandtab:shiftwidth=4:tabstop=4:
+ */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsGtkUtils_h__
+#define nsGtkUtils_h__
+
+#include <glib.h>
+
+// Some gobject functions expect functions for gpointer arguments.
+// gpointer is void* but C++ doesn't like casting functions to void*.
+template<class T> static inline gpointer
+FuncToGpointer(T aFunction)
+{
+    return reinterpret_cast<gpointer>
+        (reinterpret_cast<uintptr_t>
+         // This cast just provides a warning if T is not a function.
+         (reinterpret_cast<void (*)()>(aFunction)));
+}
+
+#endif // nsGtkUtils_h__