Use C++11 features in core/html

Source/core/html/RadioNodeList.cpp

Index: Source/core/html/RadioNodeList.cpp
diff --git a/Source/core/html/RadioNodeList.cpp b/Source/core/html/RadioNodeList.cpp
index 478de82f9b6488a39656040fa12a07ab77ef5d36..3b57208939967fcc1d1239ad822e5343a0a26d59 100644
--- a/Source/core/html/RadioNodeList.cpp
+++ b/Source/core/html/RadioNodeList.cpp
@@ -55,10 +55,10 @@ RadioNodeList::~RadioNodeList()
 static inline HTMLInputElement* toRadioButtonInputElement(Element& element)
 {
     if (!isHTMLInputElement(element))
-        return 0;
+        return nullptr;
     HTMLInputElement& inputElement = toHTMLInputElement(element);
     if (inputElement.type() != InputTypeNames::radio || inputElement.value().isEmpty())
-        return 0;
+        return nullptr;
     return &inputElement;
 }