Revert 157959 "Introduce a new reference graph to SVG*TearOffs."

Source/core/svg/properties/SVGPropertyTearOff.h

Index: Source/core/svg/properties/SVGPropertyTearOff.h
diff --git a/Source/core/svg/properties/SVGPropertyTearOff.h b/Source/core/svg/properties/SVGPropertyTearOff.h
index 8866bcc71d42dff0451423ed12bf56cb9cf0dde3..0d3b45ce7b1e8a5863739e46441cd5cc21894a81 100644
--- a/Source/core/svg/properties/SVGPropertyTearOff.h
+++ b/Source/core/svg/properties/SVGPropertyTearOff.h
@@ -74,8 +74,7 @@ public:
     {
         if (!m_animatedProperty || m_valueIsCopy)
             return 0;
-        ASSERT(m_contextElement);
-        return m_contextElement;
+        return m_contextElement.get();
     }
 
     void addChild(WeakPtr<SVGPropertyTearOffBase> child)
@@ -155,7 +154,7 @@ protected:
         m_childTearOffs.clear();
     }
 
-    SVGElement* m_contextElement;
+    RefPtr<SVGElement> m_contextElement;
     SVGAnimatedProperty* m_animatedProperty;
     SVGPropertyRole m_role;
     PropertyType* m_value;