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

Source/core/svg/SVGElement.h

Index: Source/core/svg/SVGElement.h
diff --git a/Source/core/svg/SVGElement.h b/Source/core/svg/SVGElement.h
index 01026b14651f18a40170df0c8d997931906a496b..f401221e664a1d3bf44d89c23baeb434a70a0008 100644
--- a/Source/core/svg/SVGElement.h
+++ b/Source/core/svg/SVGElement.h
@@ -139,6 +139,9 @@ public:
 
     void invalidateRelativeLengthClients(SubtreeLayoutScope* = 0);
 
+    bool isContextElement() const { return m_isContextElement; }
+    void setContextElement() { m_isContextElement = true; }
+
 protected:
     SVGElement(const QualifiedName&, Document&, ConstructionType = CreateSVGElement);
 
@@ -217,6 +220,7 @@ private:
     bool m_inRelativeLengthClientsInvalidation;
 #endif
     bool m_animatedPropertiesDestructed;
+    bool m_isContextElement;
 };
 
 struct SVGAttributeHashTranslator {