Oilpan: have CSSImageGeneratorValue use SelfKeepAlive<>.

Source/core/css/CSSImageGeneratorValue.h

 /*
  * Copyright (C) 2008 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 66 matching lines @@
     const LayoutObjectSizeCountMap& clients() const { return m_clients; }
 
     HashCountedSet<IntSize> m_sizes; // A count of how many times a given image size is in use.
     LayoutObjectSizeCountMap m_clients; // A map from LayoutObjects (with entry count) to image sizes.
     HashMap<IntSize, RefPtr<Image>> m_images; // A cache of Image objects by image size.
 
 #if ENABLE(OILPAN)
     // FIXME: Oilpan: when/if we can make the layoutObject point directly to the CSSImageGenerator value using
     // a member we don't need to have this hack where we keep a persistent to the instance as long as
     // there are clients in the LayoutObjectSizeCountMap.
-    GC_PLUGIN_IGNORE("366546")
-    OwnPtr<Persistent<CSSImageGeneratorValue>> m_keepAlive;
+    SelfKeepAlive<CSSImageGeneratorValue> m_keepAlive;
 #endif
 };
 
 DEFINE_CSS_VALUE_TYPE_CASTS(CSSImageGeneratorValue, isImageGeneratorValue());
 
 } // namespace blink
 
 #endif // CSSImageGeneratorValue_h