Mac: Update scrollbar size and input position during impl-overscroll

Source/platform/scroll/Scrollbar.h

 /*
  * Copyright (C) 2004, 2006 Apple Computer, Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 126 matching lines @@
     virtual IntRect convertFromContainingView(const IntRect&) const override;
 
     virtual IntPoint convertToContainingView(const IntPoint&) const override;
     virtual IntPoint convertFromContainingView(const IntPoint&) const override;
 
     void moveThumb(int pos, bool draggingDocument = false);
 
     virtual bool isAlphaLocked() const override { return m_isAlphaLocked; }
     virtual void setIsAlphaLocked(bool flag) override { m_isAlphaLocked = flag; }
 
+    virtual float elasticOverscroll() const override { return m_elasticOverscroll; }
+    virtual void setElasticOverscroll(float elasticOverscroll) override { m_elasticOverscroll = elasticOverscroll; }
+
     bool overlapsResizer() const { return m_overlapsResizer; }
     void setOverlapsResizer(bool overlapsResizer) { m_overlapsResizer = overlapsResizer; }
 
     DisplayItemClient displayItemClient() const { return static_cast<DisplayItemClientInternalVoid*>((void*)this); }
 
 protected:
     Scrollbar(ScrollableArea*, ScrollbarOrientation, ScrollbarControlSize, ScrollbarTheme* = 0);
 
     void updateThumb();
     virtual void updateThumbPosition();
@@ skipping 32 matching lines @@
 
     bool m_enabled;
 
     Timer<Scrollbar> m_scrollTimer;
     bool m_overlapsResizer;
 
     bool m_suppressInvalidation;
 
     bool m_isAlphaLocked;
 
+    float m_elasticOverscroll;
+
 private:
     virtual bool isScrollbar() const override { return true; }
 
     float scrollableAreaCurrentPos() const;
 };
 
 DEFINE_TYPE_CASTS(Scrollbar, Widget, widget, widget->isScrollbar(), widget.isScrollbar());
 
 } // namespace blink
 
 #endif // Scrollbar_h