Recalc custom scrollbar style.

Source/core/layout/LayoutBox.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 217 matching lines @@
         LayoutObject* parentToInvalidate = parent();
         for (unsigned i = 0; i < backgroundObscurationTestMaxDepth && parentToInvalidate; ++i) {
             parentToInvalidate->invalidateBackgroundObscurationStatus();
             parentToInvalidate = parentToInvalidate->parent();
         }
     }
 
     if (isDocumentElement() || isBody()) {
         document().view()->recalculateScrollbarOverlayStyle();
         document().view()->recalculateCustomScrollbarStyle();
+        LayoutView* layoutView = view();
+        bool rootLayerScrolls = document().settings() && document().settings()->rootLayerScrolls();

[skobes, 2015/08/26 18:56:08]

I think you don't need to check the root layer scrolls setting.  If it's not
enabled, the LayoutView's ScrollableArea will not have scrollbars anyway.

+        if (layoutView && rootLayerScrolls) {
+            if (DeprecatedPaintLayerScrollableArea* scrollableArea = layoutView->scrollableArea()) {
+                if (scrollableArea->horizontalScrollbar() && scrollableArea->horizontalScrollbar()->isCustomScrollbar())
+                    scrollableArea->horizontalScrollbar()->styleChanged();
+                if (scrollableArea->verticalScrollbar() && scrollableArea->verticalScrollbar()->isCustomScrollbar())
+                    scrollableArea->verticalScrollbar()->styleChanged();
+            }
+        }
     }
+
     updateShapeOutsideInfoAfterStyleChange(*style(), oldStyle);
     updateGridPositionAfterStyleChange(oldStyle);
 
     if (LayoutMultiColumnSpannerPlaceholder* placeholder = this->spannerPlaceholder())
         placeholder->layoutObjectInFlowThreadStyleDidChange(oldStyle);
 
     updateSlowRepaintStatusAfterStyleChange();
 }
 
 void LayoutBox::updateSlowRepaintStatusAfterStyleChange()
@@ skipping 4487 matching lines @@
     StyleImage* borderImage = style()->borderImage().image();
     return borderImage && borderImage->canRender(*this, style()->effectiveZoom()) && borderImage->isLoaded();
 }
 
 ShapeOutsideInfo* LayoutBox::shapeOutsideInfo() const
 {
     return ShapeOutsideInfo::isEnabledFor(*this) ? ShapeOutsideInfo::info(*this) : nullptr;
 }
 
 } // namespace blink