[svg] TearOffs dynamically hold on to the current contextElement().

Source/core/svg/SVGElement.h

 /*
  * Copyright (C) 2004, 2005, 2006, 2008 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006 Rob Buis <buis@kde.org>
  * Copyright (C) 2009 Apple Inc. 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 @@
 
     virtual bool haveLoadedRequiredResources();
 
     virtual bool addEventListener(const AtomicString& eventType, PassRefPtr<EventListener>, bool useCapture) OVERRIDE;
     virtual bool removeEventListener(const AtomicString& eventType, EventListener*, bool useCapture) OVERRIDE;
 
     virtual bool shouldMoveToFlowThread(RenderStyle*) const OVERRIDE;
 
     void invalidateRelativeLengthClients(SubtreeLayoutScope* = 0);
 
+    bool isContextElement() const { return m_isContextElement; }
+    void setContextElement() { m_isContextElement = true; }
+
 protected:
     SVGElement(const QualifiedName&, Document&, ConstructionType = CreateSVGElement);
 
     virtual void parseAttribute(const QualifiedName&, const AtomicString&) OVERRIDE;
 
     virtual void finishParsingChildren();
     virtual void attributeChanged(const QualifiedName&, const AtomicString&, AttributeModificationReason = ModifiedDirectly) OVERRIDE;
     virtual bool childShouldCreateRenderer(const Node& child) const OVERRIDE;
 
     virtual bool isPresentationAttribute(const QualifiedName&) const OVERRIDE;
@@ skipping 58 matching lines @@
     HashSet<SVGElement*> m_elementsWithRelativeLengths;
 
     BEGIN_DECLARE_ANIMATED_PROPERTIES(SVGElement)
         DECLARE_ANIMATED_STRING(ClassName, className)
     END_DECLARE_ANIMATED_PROPERTIES
 
 #if !ASSERT_DISABLED
     bool m_inRelativeLengthClientsInvalidation;
 #endif
     bool m_animatedPropertiesDestructed;
+    bool m_isContextElement;
 };
 
 struct SVGAttributeHashTranslator {
     static unsigned hash(const QualifiedName& key)
     {
         if (key.hasPrefix()) {
             QualifiedNameComponents components = { nullAtom.impl(), key.localName().impl(), key.namespaceURI().impl() };
             return hashComponents(components);
         }
         return DefaultHash<QualifiedName>::Hash::hash(key);
     }
     static bool equal(const QualifiedName& a, const QualifiedName& b) { return a.matches(b); }
 };
 
 DEFINE_NODE_TYPE_CASTS(SVGElement, isSVGElement());
 
 }
 
 #endif