Recalc custom scrollbar style.

Source/core/layout/LayoutBox.cpp

Index: Source/core/layout/LayoutBox.cpp
diff --git a/Source/core/layout/LayoutBox.cpp b/Source/core/layout/LayoutBox.cpp
index aff8b7f4339afcf14c19215ae9c50f6b2c768c16..719e52aaf92a0007cba16d76f627563ce9e43d64 100644
--- a/Source/core/layout/LayoutBox.cpp
+++ b/Source/core/layout/LayoutBox.cpp
@@ -235,7 +235,18 @@ void LayoutBox::styleDidChange(StyleDifference diff, const ComputedStyle* oldSty
     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);