Oilpan: Fix a cycle caused by SVGPropertyTearOffBase::m_contextElement

Source/core/svg/properties/SVGPropertyTearOff.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 80 matching lines @@
         ASSERT(contextElement);
         ASSERT(attributeName != QualifiedName::null());
         m_contextElement = contextElement;
         m_attributeName = attributeName;
     }
 
     virtual AnimatedPropertyType type() const = 0;
 
     DEFINE_INLINE_VIRTUAL_TRACE()
     {
-        visitor->trace(m_contextElement);
     }
 
 protected:
     SVGPropertyTearOffBase(SVGElement* contextElement, PropertyIsAnimValType propertyIsAnimVal, const QualifiedName& attributeName = QualifiedName::null())
         : m_contextElement(contextElement)
         , m_propertyIsAnimVal(propertyIsAnimVal)
         , m_isReadOnlyProperty(false)
         , m_attributeName(attributeName)
     {
     }
 
 private:
-    // These references are kept alive from V8 wrapper to prevent reference cycles
-    RawPtrWillBeMember<SVGElement> m_contextElement;
+    // This raw pointer is safe since the SVG element is guaranteed to be kept
+    // alive by a V8 wrapper.
+    GC_PLUGIN_IGNORE("crbug.com/528275")
+    SVGElement* m_contextElement;
 
     PropertyIsAnimValType m_propertyIsAnimVal;
     bool m_isReadOnlyProperty;
     QualifiedName m_attributeName;
 };
 
 template <typename Property>
 class SVGPropertyTearOff : public SVGPropertyTearOffBase {
 public:
     Property* target()
@@ skipping 25 matching lines @@
         ASSERT(m_target);
     }
 
 private:
     RefPtrWillBeMember<Property> m_target;
 };
 
 }
 
 #endif // SVGPropertyTearOff_h