Add Element::subResourceAttributeName() virtual function

Source/core/html/HTMLBodyElement.cpp

Index: Source/core/html/HTMLBodyElement.cpp
diff --git a/Source/core/html/HTMLBodyElement.cpp b/Source/core/html/HTMLBodyElement.cpp
index 60317bf593f824e1467b70f75aa20e70b1425b5a..646d4db49fcf4a38965438ab2bc7777f1b88fa1e 100644
--- a/Source/core/html/HTMLBodyElement.cpp
+++ b/Source/core/html/HTMLBodyElement.cpp
@@ -184,6 +184,11 @@ bool HTMLBodyElement::hasLegalLinkAttribute(const QualifiedName& name) const
     return name == backgroundAttr || HTMLElement::hasLegalLinkAttribute(name);
 }
 
+const QualifiedName& HTMLBodyElement::subResourceAttributeName() const
+{
+    return backgroundAttr;
+}
+
 bool HTMLBodyElement::supportsFocus() const
 {
     // This override is needed because the inherited method bails if the parent is editable.