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

Source/core/layout/svg/LayoutSVGHiddenContainer.h

 /*
  * Copyright (C) 2007 Eric Seidel <eric@webkit.org>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 23 matching lines @@
 
     virtual const char* name() const override { return "LayoutSVGHiddenContainer"; }
 
 protected:
     virtual void layout() override;
 
     virtual bool isOfType(LayoutObjectType type) const override { return type == LayoutObjectSVGHiddenContainer || LayoutSVGContainer::isOfType(type); }
 
 private:
     virtual void paint(const PaintInfo&, const LayoutPoint&) override final;
-    virtual LayoutRect clippedOverflowRectForPaintInvalidation(const LayoutBoxModelObject*, const PaintInvalidationState* = 0) const override final { return LayoutRect(); }
+    virtual LayoutRect clippedOverflowRectForPaintInvalidation(const LayoutBoxModelObject*, const PaintInvalidationState* = nullptr) const override final { return LayoutRect(); }
     virtual void absoluteQuads(Vector<FloatQuad>&, bool* wasFixed) const override final;
 
     virtual bool nodeAtFloatPoint(HitTestResult&, const FloatPoint& pointInParent, HitTestAction) override final;
 };
 }
 
 #endif // LayoutSVGHiddenContainer_h