Issue repaints when offsetFromRenderer changes for any squashed layer.

Source/core/rendering/compositing/CompositedLayerMapping.h

 /*
  * Copyright (C) 2009, 2010, 2011 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 30 matching lines @@
 struct GraphicsLayerPaintInfo {
     RenderLayer* renderLayer;
 
     LayoutRect compositedBounds;
 
     // The clip rect to apply, in the local coordinate space of the squashed layer, when painting it.
     IntRect localClipRectForSquashedLayer;
 
     // Offset describing where this squashed RenderLayer paints into the shared GraphicsLayer backing.
     IntSize offsetFromRenderer;
+    bool offsetFromRendererSet;
+
     LayoutSize subpixelAccumulation;
 
     GraphicsLayerPaintingPhase paintingPhase;
 
     bool isBackgroundLayer;
 
+    GraphicsLayerPaintInfo() : offsetFromRendererSet(false) { }

[Ian Vollick, 2014/06/13 02:42:48]

How would you feel about adding an initializer for isBackgroundLayer and
renderLayer while you're there?

[chrishtr, 2014/06/13 04:24:24]

Done.

+
     bool isEquivalentForSquashing(const GraphicsLayerPaintInfo& other)
     {
         // FIXME: offsetFromRenderer and compositedBounds should not be checked here, because
         // they are not yet fixed at the time this function is used.
         return renderLayer == other.renderLayer
             && paintingPhase == other.paintingPhase
             && isBackgroundLayer == other.isBackgroundLayer;
     }
 };
 
@@ skipping 326 matching lines @@
     bool m_requiresOwnBackingStoreForAncestorReasons : 1;
     bool m_canCompositeFilters : 1;
     bool m_backgroundLayerPaintsFixedRootBackground : 1;
     bool m_needToUpdateGraphicsLayer : 1;
     bool m_needToUpdateGraphicsLayerOfAllDecendants : 1;
 };
 
 } // namespace WebCore
 
 #endif // CompositedLayerMapping_h