Fix paint invalidation rect tracking within composited scrolling layers.

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 1172 matching lines @@
 
     // When this object is invalidated for paint, this method is called to invalidate any DisplayItemClients
     // owned by this object, including the object itself, LayoutText/LayoutInline line boxes, etc.,
     // not including children which will be invalidated normally during invalidateTreeIfNeeded() and
     // parts which are invalidated separately (e.g. scrollbars).
     virtual void invalidateDisplayItemClients(const LayoutBoxModelObject& paintInvalidationContainer) const;
 
     void setIsSlowRepaintObject(bool);
 
 private:
+    // Adjusts a paint invalidation rect in the space of |m_previousPaintInvalidationRect| and |m_previousPositionFromPaintInvalidationBacking|
+    // to be in the space of the |paintInvalidationContainer|,
+    // if needed. They can be different only if |paintInvalidationContainer| is a composited scroller.
+    void adjustInvalidationRectForCompositedScrolling(LayoutRect&, const LayoutBoxModelObject& paintInvalidationContainer);
+
     void clearLayoutRootIfNeeded() const;
 
     bool isInert() const;
 
     void updateImage(StyleImage*, StyleImage*);
 
     void scheduleRelayout();
 
     void updateShapeImage(const ShapeValue*, const ShapeValue*);
     void updateFillImages(const FillLayer* oldLayers, const FillLayer& newLayers);
@@ skipping 216 matching lines @@
     void setIsDragging(bool b) { m_bitfields.setIsDragging(b); }
     void setEverHadLayout(bool b) { m_bitfields.setEverHadLayout(b); }
     void setShouldInvalidateOverflowForPaint(bool b) { m_bitfields.setShouldInvalidateOverflowForPaint(b); }
     void setSelfNeedsOverflowRecalcAfterStyleChange(bool b) { m_bitfields.setSelfNeedsOverflowRecalcAfterStyleChange(b); }
     void setChildNeedsOverflowRecalcAfterStyleChange(bool b) { m_bitfields.setChildNeedsOverflowRecalcAfterStyleChange(b); }
 
 private:
     // Store state between styleWillChange and styleDidChange
     static bool s_affectsParentBlock;
 
-    // This stores the paint invalidation rect from the previous frame.
+    // This stores the paint invalidation rect from the previous frame. This rect does *not* account for composited scrolling. See

[skobes, 2015/08/13 21:26:10]

It's a little unclear what it means to "account for composited scrolling". 
Could we just say that "the rect is in the coordinate space of the paint
invalidation container's scrolling contents layer"?

+    // adjustInvalidationRectForCompositedScrolling().
     LayoutRect m_previousPaintInvalidationRect;
 
     // This stores the position in the paint invalidation backing's coordinate.
     // It is used to detect layoutObject shifts that forces a full invalidation.
+    // This point does *not* account for composited scrolling. See adjustInvalidationRectForCompositedScrolling().
     LayoutPoint m_previousPositionFromPaintInvalidationBacking;
 };
 
 // FIXME: remove this once the layout object lifecycle ASSERTS are no longer hit.
 class DeprecatedDisableModifyLayoutTreeStructureAsserts {
     WTF_MAKE_NONCOPYABLE(DeprecatedDisableModifyLayoutTreeStructureAsserts);
 public:
     DeprecatedDisableModifyLayoutTreeStructureAsserts();
 
     static bool canModifyLayoutTreeStateInAnyState();
@@ skipping 213 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