Replace elementHasLegalLinkAttribute() helper with virtual function

Source/core/html/HTMLFormElement.cpp

Index: Source/core/html/HTMLFormElement.cpp
diff --git a/Source/core/html/HTMLFormElement.cpp b/Source/core/html/HTMLFormElement.cpp
index 0c96bf045d7b7197b84f9f21cb2846b261469db5..3af938fb073806ab4bd1bf87d9d9a5e249834468 100644
--- a/Source/core/html/HTMLFormElement.cpp
+++ b/Source/core/html/HTMLFormElement.cpp
@@ -512,6 +512,11 @@ bool HTMLFormElement::isURLAttribute(const Attribute& attribute) const
     return attribute.name() == actionAttr || HTMLElement::isURLAttribute(attribute);
 }
 
+bool HTMLFormElement::hasLegalLinkAttribute(const QualifiedName& name) const
+{
+    return name == actionAttr || HTMLElement::hasLegalLinkAttribute(name);
+}
+
 void HTMLFormElement::associate(HTMLImageElement& e)
 {
     m_imageElementsAreDirty = true;