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

Source/core/layout/LayoutTableCol.cpp

Index: Source/core/layout/LayoutTableCol.cpp
diff --git a/Source/core/layout/LayoutTableCol.cpp b/Source/core/layout/LayoutTableCol.cpp
index 73cf46dd452d94d3a96f7b9e5add71f4f5957fa1..efb55a11e40a7e413b5a4dc0fe2a1285d578431b 100644
--- a/Source/core/layout/LayoutTableCol.cpp
+++ b/Source/core/layout/LayoutTableCol.cpp
@@ -141,13 +141,13 @@ LayoutTable* LayoutTableCol::table() const
     LayoutObject* table = parent();
     if (table && !table->isTable())
         table = table->parent();
-    return table && table->isTable() ? toLayoutTable(table) : 0;
+    return table && table->isTable() ? toLayoutTable(table) : nullptr;
 }
 
 LayoutTableCol* LayoutTableCol::enclosingColumnGroup() const
 {
     if (!parent()->isLayoutTableCol())
-        return 0;
+        return nullptr;
 
     LayoutTableCol* parentColumnGroup = toLayoutTableCol(parent());
     ASSERT(parentColumnGroup->isTableColumnGroup());