Replace elementHasLegalLinkAttribute() helper with virtual function

Source/core/html/HTMLTableCellElement.cpp

Index: Source/core/html/HTMLTableCellElement.cpp
diff --git a/Source/core/html/HTMLTableCellElement.cpp b/Source/core/html/HTMLTableCellElement.cpp
index 9e0b4f1a9a3798edf8c9318286e0568b2de17427..489965c443bb7d9d2d619b2f7a3f6d91e3da8a7b 100644
--- a/Source/core/html/HTMLTableCellElement.cpp
+++ b/Source/core/html/HTMLTableCellElement.cpp
@@ -128,6 +128,11 @@ bool HTMLTableCellElement::isURLAttribute(const Attribute& attribute) const
     return attribute.name() == backgroundAttr || HTMLTablePartElement::isURLAttribute(attribute);
 }
 
+bool HTMLTableCellElement::hasLegalLinkAttribute(const QualifiedName& name) const
+{
+    return (hasLocalName(tdTag) && name == backgroundAttr) || HTMLTablePartElement::hasLegalLinkAttribute(name);
+}
+
 const AtomicString& HTMLTableCellElement::abbr() const
 {
     return fastGetAttribute(abbrAttr);