Create custom scrollbars when html element has overflow:scroll

Source/core/paint/DeprecatedPaintLayerScrollableArea.h

 /*
  * Copyright (C) 2003, 2009, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 216 matching lines @@
 
 private:
     explicit DeprecatedPaintLayerScrollableArea(DeprecatedPaintLayer&);
 
     bool hasHorizontalOverflow() const;
     bool hasVerticalOverflow() const;
     bool hasScrollableHorizontalOverflow() const;
     bool hasScrollableVerticalOverflow() const;
     bool visualViewportSuppliesScrollbars() const;
 
+    bool needsScrollbarReconstruction() const;
+
     void computeScrollDimensions();
 
     // TODO(bokan): This method hides the base class version and is subtly different.
     // Should be unified.
     DoubleSize clampScrollOffset(const DoubleSize&) const;
 
     void setScrollOffset(const IntPoint&, ScrollType) override;
     void setScrollOffset(const DoublePoint&, ScrollType) override;
 
     LayoutUnit verticalScrollbarStart(int minX, int maxX) const;
@@ skipping 51 matching lines @@
     LayoutScrollbarPart* m_resizer;
 
 #if ENABLE(ASSERT)
     bool m_hasBeenDisposed;
 #endif
 };
 
 } // namespace blink
 
 #endif // LayerScrollableArea_h