Adding a scrollbar listener object, so I can be notified.

layout/xul/base/src/nsIScrollbarListener.h

@@ -0,0 +1,40 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * The contents of this file are subject to the Netscape Public License
+ * Version 1.0 (the "License"); you may not use this file except in
+ * compliance with the License.  You may obtain a copy of the License at
+ * http://www.mozilla.org/NPL/
+ *
+ * Software distributed under the License is distributed on an "AS IS"
+ * basis, WITHOUT WARRANTY OF ANY KIND, either express or implied.  See
+ * the License for the specific language governing rights and limitations
+ * under the License.
+ *
+ * The Original Code is Mozilla Communicator client code.
+ *
+ * The Initial Developer of the Original Code is Netscape Communications
+ * Corporation.  Portions created by Netscape are Copyright (C) 1998
+ * Netscape Communications Corporation.  All Rights Reserved.
+ */
+
+#ifndef nsIScrollbarListener_h___
+#define nsIScrollbarListener_h___
+
+// {A0ADBD81-2911-11d3-97FA-00400553EEF0}
+#define NS_ISCROLLBARLISTENER_IID \
+{ 0xa0adbd81, 0x2911, 0x11d3, { 0x97, 0xfa, 0x0, 0x40, 0x5, 0x53, 0xee, 0xf0 } }
+
+static NS_DEFINE_IID(kIScrollbarListenerIID,     NS_ISCROLLBARLISTENER_IID);
+
+class nsIScrollbarListener : public nsISupports {
+
+public:
+
+  static const nsIID& GetIID() { static nsIID iid = NS_ISCROLLBARLISTENER_IID; return iid; }
+  
+  NS_IMETHOD PositionChanged(PRInt32 aOldIndex, PRInt32 aNewIndex) = 0;
+
+};
+
+#endif
+