Mark when we may have been invalidated to early out on repaintTreeAfterLayout.

Source/core/rendering/RenderScrollbarPart.cpp

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 38 matching lines @@
 
 RenderScrollbarPart* RenderScrollbarPart::createAnonymous(Document* document, RenderScrollbar* scrollbar, ScrollbarPart part)
 {
     RenderScrollbarPart* renderer = new RenderScrollbarPart(scrollbar, part);
     renderer->setDocumentForAnonymous(document);
     return renderer;
 }
 
 void RenderScrollbarPart::layout()
 {
+    setMayNeedInvalidation(true);
     setLocation(LayoutPoint()); // We don't worry about positioning ourselves. We're just determining our minimum width/height.
     if (m_scrollbar->orientation() == HorizontalScrollbar)
         layoutHorizontalPart();
     else
         layoutVerticalPart();
 
     clearNeedsLayout();
 }
 
 void RenderScrollbarPart::layoutHorizontalPart()
@@ skipping 126 matching lines @@
 }
 
 RenderObject* RenderScrollbarPart::rendererOwningScrollbar() const
 {
     if (!m_scrollbar)
         return 0;
     return m_scrollbar->owningRenderer();
 }
 
 }