Fix several corner case issues of scrollbar paint invalidation

third_party/WebKit/Source/core/layout/LayoutObject.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. 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 1215 matching lines @@
     virtual void computeLayerHitTestRects(LayerHitTestRects&) const;
 
     static RespectImageOrientationEnum shouldRespectImageOrientation(const LayoutObject*);
 
     bool isRelayoutBoundaryForInspector() const;
 
     // The previous paint invalidation rect, in the the space of the paint invalidation container (*not* the graphics layer that paints
     // this object).
     LayoutRect previousPaintInvalidationRectIncludingCompositedScrolling(const LayoutBoxModelObject& paintInvalidationContainer) const;
     LayoutSize previousPaintInvalidationRectSize() const { return previousPaintInvalidationRect().size(); }
-    void setPreviousPaintInvalidationRect(const LayoutRect& rect) { m_previousPaintInvalidationRect = rect; }
+
+    // Called when the previous paint invalidation rect(s) is no longer valid.
+    virtual void clearPreviousPaintInvalidationRects();
 
     // Only adjusts if the paint invalidation container is not a composited scroller.
     void adjustPreviousPaintInvalidationForScrollIfNeeded(const DoubleSize& scrollDelta);
 
     // The previous position of the top-left corner of the object in its previous paint backing.
     const LayoutPoint& previousPositionFromPaintInvalidationBacking() const
     {
         ASSERT(!RuntimeEnabledFeatures::slimmingPaintOffsetCachingEnabled());
         return m_previousPositionFromPaintInvalidationBacking;
     }
@@ skipping 177 matching lines @@
     // container, so callers should provide only the offset of the container within it's layer.
     // containerRect is a rect that has already been added for the currentLayer which is likely to
     // be a container for child elements. Any rect wholly contained by containerRect can be
     // skipped.
     virtual void addLayerHitTestRects(LayerHitTestRects&, const PaintLayer* currentLayer, const LayoutPoint& layerOffset, const LayoutRect& containerRect) const;
 
     // Add hit-test rects for this layoutObject only to the provided list. layerOffset is the offset
     // of this layoutObject within the current layer that should be used for each result.
     virtual void computeSelfHitTestRects(Vector<LayoutRect>&, const LayoutPoint& layerOffset) const { }
 
+    void setPreviousPaintInvalidationRect(const LayoutRect& rect) { m_previousPaintInvalidationRect = rect; }
+
     virtual PaintInvalidationReason paintInvalidationReason(const LayoutBoxModelObject& paintInvalidationContainer,
         const LayoutRect& oldPaintInvalidationRect, const LayoutPoint& oldPositionFromPaintInvalidationBacking,
         const LayoutRect& newPaintInvalidationRect, const LayoutPoint& newPositionFromPaintInvalidationBacking) const;
     virtual void incrementallyInvalidatePaint(const LayoutBoxModelObject& paintInvalidationContainer, const LayoutRect& oldBounds, const LayoutRect& newBounds, const LayoutPoint& positionFromPaintInvalidationBacking);
 
     virtual bool hasNonCompositedScrollbars() const { return false; }
 
 #if ENABLE(ASSERT)
     virtual bool paintInvalidationStateIsDirty() const
     {
@@ skipping 593 matching lines @@
 void showTree(const blink::LayoutObject*);
 void showLineTree(const blink::LayoutObject*);
 void showLayoutTree(const blink::LayoutObject* object1);
 // We don't make object2 an optional parameter so that showLayoutTree
 // can be called from gdb easily.
 void showLayoutTree(const blink::LayoutObject* object1, const blink::LayoutObject* object2);
 
 #endif
 
 #endif // LayoutObject_h