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

Source/core/layout/LayoutBR.h

Index: Source/core/layout/LayoutBR.h
diff --git a/Source/core/layout/LayoutBR.h b/Source/core/layout/LayoutBR.h
index 6d34d3de7a94f2bb36ad0ee36c26e169da993617..f75e74b6126f3b2e888e086913b2dc3c374492dc 100644
--- a/Source/core/layout/LayoutBR.h
+++ b/Source/core/layout/LayoutBR.h
@@ -36,10 +36,10 @@ public:
 
     virtual const char* name() const override { return "LayoutBR"; }
 
-    virtual LayoutRect selectionRectForPaintInvalidation(const LayoutBoxModelObject* /*paintInvalidationContainer*/) const override { return LayoutRect(); }
+    virtual LayoutRect selectionRectForPaintInvalidation(const LayoutBoxModelObject* /* paintInvalidationContainer */) const override { return LayoutRect(); }
 
-    virtual float width(unsigned /*from*/, unsigned /*len*/, const Font&, LayoutUnit /*xPos*/, TextDirection, HashSet<const SimpleFontData*>* = 0 /*fallbackFonts*/ , GlyphOverflow* = 0) const override { return 0; }
-    virtual float width(unsigned /*from*/, unsigned /*len*/, LayoutUnit /*xpos*/, TextDirection, bool = false /*firstLine*/, HashSet<const SimpleFontData*>* = 0 /*fallbackFonts*/, GlyphOverflow* = 0) const override { return 0; }
+    virtual float width(unsigned /* from */, unsigned /* len */, const Font&, LayoutUnit /* xpos */, TextDirection, HashSet<const SimpleFontData*>* = nullptr /* fallbackFonts */ , GlyphOverflow* = nullptr) const override { return 0; }
+    virtual float width(unsigned /* from */, unsigned /* len */, LayoutUnit /* xpos */, TextDirection, bool = false /* firstLine */, HashSet<const SimpleFontData*>* = nullptr /* fallbackFonts */, GlyphOverflow* = nullptr) const override { return 0; }
 
     int lineHeight(bool firstLine) const;