Use C++11 features in core/html

Source/core/html/HTMLTableColElement.cpp

Index: Source/core/html/HTMLTableColElement.cpp
diff --git a/Source/core/html/HTMLTableColElement.cpp b/Source/core/html/HTMLTableColElement.cpp
index 0f9bc582451a79060cc1ad373daad7e2d56803d2..662e966d4f17ad48c4fffc1a01211daf04268e2d 100644
--- a/Source/core/html/HTMLTableColElement.cpp
+++ b/Source/core/html/HTMLTableColElement.cpp
@@ -82,10 +82,10 @@ void HTMLTableColElement::parseAttribute(const QualifiedName& name, const Atomic
 const StylePropertySet* HTMLTableColElement::additionalPresentationAttributeStyle()
 {
     if (!hasTagName(colgroupTag))
-        return 0;
+        return nullptr;
     if (HTMLTableElement* table = findParentTable())
         return table->additionalGroupStyle(false);
-    return 0;
+    return nullptr;
 }
 
 void HTMLTableColElement::setSpan(int n)