Pepper and WebKit API change to support a plugin knowing if a scrollbar is an overlay one.

ppapi/c/dev/ppb_scrollbar_group_dev.h

+/* Copyright (c) 2011 The Chromium Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+#ifndef PPAPI_C_DEV_PPB_SCROLLBAR_GROUP_DEV_H_
+#define PPAPI_C_DEV_PPB_SCROLLBAR_GROUP_DEV_H_
+
+#include "ppapi/c/pp_instance.h"
+#include "ppapi/c/pp_resource.h"
+
+#define PPB_SCROLLBAR_GROUP_DEV_INTERFACE_0_1 "PPP_Scrollbar_Group(Dev);0.1"
+#define PPB_SCROLLBAR_GROUP_DEV_INTERFACE PPB_SCROLLBAR_GROUP_DEV_INTERFACE_0_1
+
+// The interface for a scrollbar group. Horizontal and vertical scrollbars for
+// the same region need to be associated together with one group. This is
+// necessary for some platforms in which changes to one scrollbar lead to
+// animation changes for the other.
+struct PPB_ScrollbarGroup_Dev {
+  // Create a new scrollbar group.  Returns 0 if the instance is invalid.
+  PP_Resource (*Create)(PP_Instance instance);
+};
+
+#endif  /* PPAPI_C_DEV_PPB_SCROLLBAR_GROUP_DEV_H_ */