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

Source/core/layout/LayoutGeometryMap.h

 /*
  * Copyright (C) 2012 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 58 matching lines @@
     void popMappingsToAncestor(const LayoutBoxModelObject*);
 
     // The following methods should only be called by layoutObjects inside a call to pushMappingsToAncestor().
 
     // Push geometry info between this layoutObject and some ancestor. The ancestor must be its container() or some
     // stacking context between the layoutObject and its container.
     void push(const LayoutObject*, const LayoutSize&, bool accumulatingTransform = false, bool isNonUniform = false, bool isFixedPosition = false, bool hasTransform = false, LayoutSize offsetForFixedPosition = LayoutSize());
     void push(const LayoutObject*, const TransformationMatrix&, bool accumulatingTransform = false, bool isNonUniform = false, bool isFixedPosition = false, bool hasTransform = false, LayoutSize offsetForFixedPosition = LayoutSize());
 
 private:
-    void mapToContainer(TransformState&, const LayoutBoxModelObject* container = 0) const;
+    void mapToContainer(TransformState&, const LayoutBoxModelObject* container = nullptr) const;
 
     void stepInserted(const LayoutGeometryMapStep&);
     void stepRemoved(const LayoutGeometryMapStep&);
 
     bool hasNonUniformStep() const { return m_nonUniformStepsCount; }
     bool hasTransformStep() const { return m_transformedStepsCount; }
     bool hasFixedPositionStep() const { return m_fixedStepsCount; }
 
 #ifndef NDEBUG
     void dumpSteps() const;
@@ skipping 10 matching lines @@
     int m_transformedStepsCount;
     int m_fixedStepsCount;
     LayoutGeometryMapSteps m_mapping;
     LayoutSize m_accumulatedOffset;
     MapCoordinatesFlags m_mapCoordinatesFlags;
 };
 
 } // namespace blink
 
 #endif // LayoutGeometryMap_h