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

Source/core/layout/LayoutTable.h

Index: Source/core/layout/LayoutTable.h
diff --git a/Source/core/layout/LayoutTable.h b/Source/core/layout/LayoutTable.h
index eb31b381e061dc9ad7d1633468b83a7857f810a3..2d335f457ae8b8cdbb86b99dd8e5332c02466b6f 100644
--- a/Source/core/layout/LayoutTable.h
+++ b/Source/core/layout/LayoutTable.h
@@ -123,8 +123,8 @@ public:
     int calcBorderEnd() const;
     void recalcBordersInRowDirection();
 
-    virtual void addChild(LayoutObject* child, LayoutObject* beforeChild = 0) override;
-    virtual void addChildIgnoringContinuation(LayoutObject* newChild, LayoutObject* beforeChild = 0) override;
+    virtual void addChild(LayoutObject* child, LayoutObject* beforeChild = nullptr) override;
+    virtual void addChildIgnoringContinuation(LayoutObject* newChild, LayoutObject* beforeChild = nullptr) override;
 
     struct ColumnStruct {
         explicit ColumnStruct(unsigned initialSpan = 1)
@@ -213,11 +213,11 @@ public:
     // Return the first column or column-group.
     LayoutTableCol* firstColumn() const;
 
-    LayoutTableCol* colElement(unsigned col, bool* startEdge = 0, bool* endEdge = 0) const
+    LayoutTableCol* colElement(unsigned col, bool* startEdge = nullptr, bool* endEdge = nullptr) const
     {
         // The common case is to not have columns, make that case fast.
         if (!m_hasColElements)
-            return 0;
+            return nullptr;
         return slowColElement(col, startEdge, endEdge);
     }