Scrollbar width is set using thickness to compute correct rect size

third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 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@gmail.com>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 931 matching lines @@
 IntRect PaintLayerScrollableArea::rectForHorizontalScrollbar(const IntRect& borderBoxRect) const
 {
     if (!hasHorizontalScrollbar())
         return IntRect();
 
     const IntRect& scrollCorner = scrollCornerRect();
 
     return IntRect(horizontalScrollbarStart(borderBoxRect.x()),
         borderBoxRect.maxY() - box().borderBottom() - horizontalScrollbar()->height(),
         borderBoxRect.width() - (box().borderLeft() + box().borderRight()) - scrollCorner.width(),
-        horizontalScrollbar()->height());
+        horizontalScrollbar()->scrollbarThickness());
 }
 
 IntRect PaintLayerScrollableArea::rectForVerticalScrollbar(const IntRect& borderBoxRect) const
 {
     if (!hasVerticalScrollbar())
         return IntRect();
 
     const IntRect& scrollCorner = scrollCornerRect();
 
     return IntRect(verticalScrollbarStart(borderBoxRect.x(), borderBoxRect.maxX()),
         borderBoxRect.y() + box().borderTop(),
-        verticalScrollbar()->width(),
+        verticalScrollbar()->scrollbarThickness(),
         borderBoxRect.height() - (box().borderTop() + box().borderBottom()) - scrollCorner.height());
 }
 
 int PaintLayerScrollableArea::verticalScrollbarStart(int minX, int maxX) const
 {
     if (box().shouldPlaceBlockDirectionScrollbarOnLogicalLeft())
         return minX + box().borderLeft();
     return maxX - box().borderRight() - verticalScrollbar()->width();
 }
 
@@ skipping 801 matching lines @@
 
 void PaintLayerScrollableArea::DelayScrollPositionClampScope::clampScrollableAreas()
 {
     for (auto& scrollableArea : *s_needsClamp)
         scrollableArea->clampScrollPositionsAfterLayout();
     delete s_needsClamp;
     s_needsClamp = nullptr;
 }
 
 } // namespace blink