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

ppapi/cpp/dev/scrollbar_dev.h

 // Copyright (c) 2010 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_CPP_DEV_SCROLLBAR_DEV_H_
 #define PPAPI_CPP_DEV_SCROLLBAR_DEV_H_
 
 #include "ppapi/c/dev/ppb_scrollbar_dev.h"
 #include "ppapi/cpp/dev/widget_dev.h"
 
 namespace pp {
 
 class Instance;
+class ScrollbarGroup_Dev;
 
 // This class allows a plugin to use the browser's scrollbar widget.
 class Scrollbar_Dev : public Widget_Dev {
  public:
   // Creates an is_null() Scrollbar object.
   Scrollbar_Dev() {}
 
   explicit Scrollbar_Dev(PP_Resource resource);
-  Scrollbar_Dev(const Instance& instance, bool vertical);
+  Scrollbar_Dev(const ScrollbarGroup_Dev& scrollbar_group,
+                bool vertical);
   Scrollbar_Dev(const Scrollbar_Dev& other);
 
   Scrollbar_Dev& operator=(const Scrollbar_Dev& other);
 
   // PPB_Scrollbar methods:
   uint32_t GetThickness();
+  bool IsOverlay();
   uint32_t GetValue();
   void SetValue(uint32_t value);
   void SetDocumentSize(uint32_t size);
   void SetTickMarks(const Rect* tick_marks, uint32_t count);
   void ScrollBy(PP_ScrollBy_Dev unit, int32_t multiplier);
 };
 
 }  // namespace pp
 
 #endif  // PPAPI_CPP_DEV_SCROLLBAR_DEV_H_