Clear scrollbar damages in time

Source/core/rendering/RenderBox.h

Index: Source/core/rendering/RenderBox.h
diff --git a/Source/core/rendering/RenderBox.h b/Source/core/rendering/RenderBox.h
index 5732f1fc13adb0c30c63799d7c50dbc0e9b06ebd..814f9bee2fac34d7da671ebcec7d286c733c2667 100644
--- a/Source/core/rendering/RenderBox.h
+++ b/Source/core/rendering/RenderBox.h
@@ -31,6 +31,7 @@
 namespace blink {
 
 struct PaintInfo;
+class RenderLayerScrollableArea;
 
 enum SizeType { MainOrPreferredSize, MinSize, MaxSize };
 enum AvailableLogicalHeightType { ExcludeMarginBorderPadding, IncludeMarginBorderPadding };
@@ -682,6 +683,11 @@ protected:
         const LayoutRect& oldBounds, const LayoutPoint& oldPositionFromPaintInvalidationContainer,
         const LayoutRect& newBounds, const LayoutPoint& newPositionFromPaintInvalidationContainer) OVERRIDE;
 
+    virtual void clearPaintInvalidationState() OVERRIDE;
+#if ENABLE(ASSERT)
+    virtual bool paintInvalidationStateIsDirty() const OVERRIDE;
+#endif
+
 private:
     void updateShapeOutsideInfoAfterStyleChange(const RenderStyle&, const RenderStyle* oldStyle);
     void updateGridPositionAfterStyleChange(const RenderStyle*);