diff -r 000000000000 -r 6474c204b198 layout/ipc/RenderFrameUtils.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/layout/ipc/RenderFrameUtils.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,46 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: sw=2 ts=8 et :
+ */
+/* 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 mozilla_layer_RenderFrameUtils_h
+#define mozilla_layer_RenderFrameUtils_h
+
+#include "ipc/IPCMessageUtils.h"
+
+namespace mozilla {
+namespace layout {
+
+enum ScrollingBehavior {
+  /**
+   * Use default scrolling behavior, which is synchronous: web content
+   * is reflowed and repainted for every scroll or zoom.
+   */
+  DEFAULT_SCROLLING,
+  /**
+   * Use asynchronous panning and zooming, in which prerendered
+   * content can be translated and scaled independently of the thread
+   * painting content, without content reflowing or repainting.
+   */
+  ASYNC_PAN_ZOOM,
+  SCROLLING_BEHAVIOR_SENTINEL
+};
+
+} // namespace layout
+} // namespace mozilla
+
+namespace IPC {
+
+template <>
+struct ParamTraits<mozilla::layout::ScrollingBehavior>
+  : public ContiguousEnumSerializer<
+             mozilla::layout::ScrollingBehavior,
+             mozilla::layout::DEFAULT_SCROLLING,
+             mozilla::layout::SCROLLING_BEHAVIOR_SENTINEL>
+{};
+
+} // namespace IPC
+
+#endif // mozilla_layer_RenderFrameUtils_h