Oilpan: add reqd tracing of ImportedStyleSheetClients.

third_party/WebKit/Source/core/css/StyleRuleImport.h

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * (C) 2002-2003 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2002, 2006, 2008, 2012 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 50 matching lines @@
     class ImportedStyleSheetClient final : public StyleSheetResourceClient {
         DISALLOW_NEW();
     public:
         ImportedStyleSheetClient(StyleRuleImport* ownerRule) : m_ownerRule(ownerRule) { }
         ~ImportedStyleSheetClient() override { }
         void setCSSStyleSheet(const String& href, const KURL& baseURL, const String& charset, const CSSStyleSheetResource* sheet) override
         {
             m_ownerRule->setCSSStyleSheet(href, baseURL, charset, sheet);
         }
         String debugName() const override { return "ImportedStyleSheetClient"; }
+
+        DEFINE_INLINE_TRACE()
+        {
+            visitor->trace(m_ownerRule);
+        }
+
     private:
-        StyleRuleImport* m_ownerRule;
+        RawPtrWillBeMember<StyleRuleImport> m_ownerRule;
     };
 
     void setCSSStyleSheet(const String& href, const KURL& baseURL, const String& charset, const CSSStyleSheetResource*);
     friend class ImportedStyleSheetClient;
 
     StyleRuleImport(const String& href, PassRefPtrWillBeRawPtr<MediaQuerySet>);
 
     RawPtrWillBeMember<StyleSheetContents> m_parentStyleSheet;
 
     ImportedStyleSheetClient m_styleSheetClient;
     String m_strHref;
     RefPtrWillBeMember<MediaQuerySet> m_mediaQueries;
     RefPtrWillBeMember<StyleSheetContents> m_styleSheet;
     ResourcePtr<CSSStyleSheetResource> m_resource;
     bool m_loading;
 };
 
 DEFINE_STYLE_RULE_TYPE_CASTS(Import);
 
 } // namespace blink
 
 #endif