Oilpan: fix build after r353261.

third_party/WebKit/Source/core/html/HTMLAreaElement.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2008, 2009, 2011 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 17 matching lines @@
 #include "platform/geometry/LayoutRect.h"
 
 namespace blink {
 
 class HitTestResult;
 class HTMLImageElement;
 class Path;
 
 class CORE_EXPORT HTMLAreaElement final : public HTMLAnchorElement {
     DEFINE_WRAPPERTYPEINFO();
+    WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(HTMLAreaElement);
 public:
     DECLARE_NODE_FACTORY(HTMLAreaElement);
 
     bool isDefault() const { return m_shape == Default; }
 
     bool pointInArea(LayoutPoint, const LayoutSize& containerSize);
 
     LayoutRect computeRect(const LayoutObject*) const;
     Path computePath(const LayoutObject*) const;
 
     // The parent map's image.
     HTMLImageElement* imageElement() const;
 
+    DEFINE_INLINE_VIRTUAL_TRACE() { HTMLAnchorElement::trace(visitor); }
+
 private:
     explicit HTMLAreaElement(Document&);
     ~HTMLAreaElement();
 
     void parseAttribute(const QualifiedName&, const AtomicString&) override;
     bool isKeyboardFocusable() const override;
     bool isMouseFocusable() const override;
     bool layoutObjectIsFocusable() const override;
     void updateFocusAppearance(bool /*restorePreviousSelection*/) override;
     void setFocus(bool) override;
 
     enum Shape { Default, Poly, Rect, Circle, Unknown };
     Path getRegion(const LayoutSize&) const;
     void invalidateCachedRegion();
 
     OwnPtr<Path> m_region;
     Vector<Length> m_coords;
     LayoutSize m_lastSize;
     Shape m_shape;
 };
 
 } // namespace blink
 
 #endif // HTMLAreaElement_h