C++11: Replace 0 with nullptr where applicable in layout code.

Source/core/layout/compositing/CompositedDeprecatedPaintLayerMapping.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 32 matching lines @@
 
     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 Layer paints into the shared GraphicsLayer backing.
     IntSize offsetFromLayoutObject;
     bool offsetFromLayoutObjectSet;
 
-    GraphicsLayerPaintInfo() : paintLayer(0), offsetFromLayoutObjectSet(false) { }
+    GraphicsLayerPaintInfo() : paintLayer(nullptr), offsetFromLayoutObjectSet(false) { }
 };
 
 enum GraphicsLayerUpdateScope {
     GraphicsLayerUpdateNone,
     GraphicsLayerUpdateLocal,
     GraphicsLayerUpdateSubtree,
 };
 
 // CompositedDeprecatedPaintLayerMapping keeps track of how Layers of the layout tree correspond to
 // GraphicsLayers of the composited layer tree. Each instance of CompositedDeprecatedPaintLayerMapping
@@ skipping 118 matching lines @@
 
     virtual String debugName(const GraphicsLayer*) override;
 
     LayoutSize contentOffsetInCompositingLayer() const;
 
     LayoutPoint squashingOffsetFromTransformedAncestor()
     {
         return m_squashingLayerOffsetFromTransformedAncestor;
     }
 
-    // If there is a squashed layer painting into this CLM that is an ancestor of the given LayoutObject, return it. Otherwise return 0.
+    // If there is a squashed layer painting into this CLM that is an ancestor of the given LayoutObject, return it. Otherwise return nullptr.
     const GraphicsLayerPaintInfo* containingSquashedLayer(const LayoutObject*, unsigned maxSquashedLayerIndex);
 
     void updateScrollingBlockSelection();
 
     DisplayItemClient displayItemClient() const { return toDisplayItemClient(this); }
     String debugName() const { return "CompositedLayerMapping for " + owningLayer().debugName(); }
 
 private:
     static const GraphicsLayerPaintInfo* containingSquashedLayer(const LayoutObject*,  const Vector<GraphicsLayerPaintInfo>& layers, unsigned maxSquashedLayerIndex);
 
@@ skipping 213 matching lines @@
     unsigned m_pendingUpdateScope : 2;
     unsigned m_isMainFrameLayoutViewLayer : 1;
 
     unsigned m_backgroundLayerPaintsFixedRootBackground : 1;
     unsigned m_scrollingContentsAreEmpty : 1;
 };
 
 } // namespace blink
 
 #endif // CompositedDeprecatedPaintLayerMapping_h