diff -r 000000000000 -r 6474c204b198 docshell/base/nsIScrollObserver.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/docshell/base/nsIScrollObserver.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,28 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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 nsIScrollObserver_h___
+#define nsIScrollObserver_h___
+
+#include "nsISupports.h"
+
+#define NS_ISCROLLOBSERVER_IID \
+  { 0x7c1a8b63, 0xe322, 0x4827, \
+    { 0xa4, 0xb1, 0x3b, 0x6e, 0x59, 0x03, 0x47, 0x7e } }
+
+class nsIScrollObserver : public nsISupports
+{
+public:
+  NS_DECLARE_STATIC_IID_ACCESSOR(NS_ISCROLLOBSERVER_IID)
+
+  /**
+   * Called when the scroll position of some element has changed.
+   */
+  virtual void ScrollPositionChanged() = 0;
+};
+
+NS_DEFINE_STATIC_IID_ACCESSOR(nsIScrollObserver, NS_ISCROLLOBSERVER_IID)
+
+#endif /* nsIScrollObserver_h___ */