Stop using SVGElementInstance in SVGElement

Source/core/svg/SVGElementInstance.cpp

 /*
  * Copyright (C) 2007, 2008 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  * Copyright (C) 2011 Torch Mobile (Beijing) Co. Ltd. All rights reserved.
  *
  * 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.
  *
@@ skipping 121 matching lines @@
 void SVGElementInstance::detach()
 {
     // Clear all pointers. When the node is detached from the shadow DOM it should be removed but,
     // due to ref counting, it may not be. So clear everything to avoid dangling pointers.
 
     for (SVGElementInstance* node = firstChild(); node; node = node->nextSibling())
         node->detach();
 
     // Deregister as instance for passed element, if we haven't already.
     if (shadowTreeElement() && m_element->instancesForElement().contains(shadowTreeElement()))
-        m_element->removeInstanceMapping(this);
+        m_element->removeInstanceMapping(shadowTreeElement());
     // DO NOT clear ref to m_element because JavaScriptCore uses it for garbage collection
 
     m_shadowTreeElement = nullptr;
 
     m_directUseElement = 0;
     m_correspondingUseElement = 0;
 
 #if !ENABLE(OILPAN)
     removeDetachedChildrenInContainer<SVGElementInstance, SVGElementInstance>(*this);
 #endif
 }
 
 void SVGElementInstance::setShadowTreeElement(SVGElement* element)
 {
     ASSERT(element);
     m_shadowTreeElement = element;
     // Register as instance for passed element.
-    m_element->mapInstanceToElement(this);
+    m_element->mapInstanceToElement(shadowTreeElement());
 
 }
 
 void SVGElementInstance::appendChild(PassRefPtr<SVGElementInstance> child)
 {
     appendChildToContainer<SVGElementInstance, SVGElementInstance>(*child, *this);
 }
 
 const AtomicString& SVGElementInstance::interfaceName() const
 {
@@ skipping 58 matching lines @@
     visitor->trace(m_parentInstance);
     visitor->trace(m_element);
     visitor->trace(m_shadowTreeElement);
     visitor->trace(m_previousSibling);
     visitor->trace(m_nextSibling);
     visitor->trace(m_firstChild);
     visitor->trace(m_lastChild);
 }
 
 }