Remove Node.prefix so it's no longer visible to script.

Source/core/dom/Attr.h

Index: Source/core/dom/Attr.h
diff --git a/Source/core/dom/Attr.h b/Source/core/dom/Attr.h
index 604b3abc1917a77ea8a1d2751ce77cbd4217ccfe..c5103520c2cf5191f7b8b3d2782cf036b4e2aca0 100644
--- a/Source/core/dom/Attr.h
+++ b/Source/core/dom/Attr.h
@@ -63,9 +63,9 @@ public:
 
     virtual const AtomicString& localName() const OVERRIDE { return m_name.localName(); }
     virtual const AtomicString& namespaceURI() const OVERRIDE { return m_name.namespaceURI(); }
-    virtual const AtomicString& prefix() const OVERRIDE { return m_name.prefix(); }
+    virtual const AtomicString& prefix() const OVERRIDE FINAL { return m_name.prefix(); }
 
-    virtual void setPrefix(const AtomicString&, ExceptionState&) OVERRIDE;
+    void setPrefix(const AtomicString&, ExceptionState&);
 
 private:
     Attr(Element&, const QualifiedName&);