Avoid a SVG property list-induced leak (Oilpan).

Source/core/svg/properties/SVGProperty.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 70 matching lines @@
     }
 
     void setOwnerList(SVGPropertyBase* ownerList)
     {
         // Previous owner list must be cleared before setting new owner list.
         ASSERT((!ownerList && m_ownerList) || (ownerList && !m_ownerList));
 
         m_ownerList = ownerList;
     }
 
-    DEFINE_INLINE_VIRTUAL_TRACE()
-    {
-        visitor->trace(m_ownerList);
-    }
+    DEFINE_INLINE_VIRTUAL_TRACE() { }
 
 protected:
     explicit SVGPropertyBase(AnimatedPropertyType type)
         : m_type(type)
         , m_ownerList(nullptr)
     {
     }
 
 private:
     const AnimatedPropertyType m_type;
 
-    RawPtrWillBeMember<SVGPropertyBase> m_ownerList;
+    // Oilpan: the back reference to the owner should be a Member, but this can create
+    // cycles when SVG properties meet the off-heap InterpolationValue hierarchy.
+    // Not tracing it is safe, albeit an undesirable state of affairs.
+    GC_PLUGIN_IGNORE("528275")
+    SVGPropertyBase* m_ownerList;
 };
 
 }
 
 #endif // SVGProperty_h