Call scrollbarsChanged in PLSA::updateAfterStyleChange.

third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.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 488 matching lines @@
   int verticalScrollbarStart(int minX, int maxX) const;
   int horizontalScrollbarStart(int minX) const;
   IntSize scrollbarOffset(const Scrollbar&) const;
 
   enum ComputeScrollbarExistenceOption { Default, ForbidAddingAutoBars };
   void computeScrollbarExistence(
       bool& needsHorizontalScrollbar,
       bool& needsVerticalScrollbar,
       ComputeScrollbarExistenceOption = Default) const;
 
-  void setHasHorizontalScrollbar(bool hasScrollbar);
-  void setHasVerticalScrollbar(bool hasScrollbar);
+  // Returns true iff scrollbar existence changed.
+  bool setHasHorizontalScrollbar(bool hasScrollbar);
+  bool setHasVerticalScrollbar(bool hasScrollbar);
 
   void updateScrollCornerStyle();
 
   // See comments on isPointInResizeControl.
   void updateResizerAreaSet();
   void updateResizerStyle();
 
   void updateScrollableAreaSet(bool hasOverflow);
 
   void updateCompositingLayersAfterScroll();
@@ skipping 64 matching lines @@
 
 DEFINE_TYPE_CASTS(PaintLayerScrollableArea,
                   ScrollableArea,
                   scrollableArea,
                   scrollableArea->isPaintLayerScrollableArea(),
                   scrollableArea.isPaintLayerScrollableArea());
 
 }  // namespace blink
 
 #endif  // LayerScrollableArea_h