Remove some dead code in SVG "mixins"

third_party/WebKit/Source/core/svg/SVGCursorElement.h

 /*
  * Copyright (C) 2004, 2005, 2006, 2008 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006 Rob Buis <buis@kde.org>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 36 matching lines @@
     void removeReferencedElement(SVGElement*);
 
     SVGAnimatedLength* x() const { return m_x.get(); }
     SVGAnimatedLength* y() const { return m_y.get(); }
 
     DECLARE_VIRTUAL_TRACE();
 
 private:
     explicit SVGCursorElement(Document&);
 
-    bool isValid() const override { return SVGTests::isValid(document()); }
+    bool isValid() const override { return SVGTests::isValid(); }
 
     void svgAttributeChanged(const QualifiedName&) override;
 
     bool layoutObjectIsNeeded(const ComputedStyle&) override { return false; }
 
     RefPtrWillBeMember<SVGAnimatedLength> m_x;
     RefPtrWillBeMember<SVGAnimatedLength> m_y;
 
     WillBeHeapHashSet<RawPtrWillBeWeakMember<SVGElement>> m_clients;
 };
 
 } // namespace blink
 
 #endif // SVGCursorElement_h