add missing file

gtk2_ardour/line_merger.h

@@ -0,0 +1,31 @@
+/*
+ * Copyright (C) 2023 Paul Davis <paul@linuxaudiosystems.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef __gtk2_ardour_line_merger__
+#define __gtk2_ardour_line_merger__
+
+class MergeableLine;
+
+class LineMerger 
+{
+   public:
+	virtual ~LineMerger() {}
+	virtual MergeableLine* make_merger () = 0;
+};
+
+#endif /* __gtk2_ardour_line_merger__ */