Oilpan: move SVG property hierarchy to the heap.

Source/core/svg/SVGLinearGradientElement.h

 /*
  * Copyright (C) 2004, 2005, 2006, 2008 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006 Rob Buis <buis@kde.org>
  *
  * 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.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  */
 
 #ifndef SVGLinearGradientElement_h
 #define SVGLinearGradientElement_h
 
 #include "core/SVGNames.h"
 #include "core/svg/SVGAnimatedLength.h"
 #include "core/svg/SVGGradientElement.h"
+#include "platform/heap/Handle.h"
 
 namespace blink {
 
 struct LinearGradientAttributes;
 
 class SVGLinearGradientElement final : public SVGGradientElement {
     DEFINE_WRAPPERTYPEINFO();
 public:
     DECLARE_NODE_FACTORY(SVGLinearGradientElement);
 
     bool collectGradientAttributes(LinearGradientAttributes&);
 
     SVGAnimatedLength* x1() const { return m_x1.get(); }
     SVGAnimatedLength* y1() const { return m_y1.get(); }
     SVGAnimatedLength* x2() const { return m_x2.get(); }
     SVGAnimatedLength* y2() const { return m_y2.get(); }
 
+    virtual void trace(Visitor*) override;
+
 private:
     explicit SVGLinearGradientElement(Document&);
 
     bool isSupportedAttribute(const QualifiedName&);
     virtual void parseAttribute(const QualifiedName&, const AtomicString&) override;
     virtual void svgAttributeChanged(const QualifiedName&) override;
 
     virtual RenderObject* createRenderer(RenderStyle*) override;
 
     virtual bool selfHasRelativeLengths() const override;
 
-    RefPtr<SVGAnimatedLength> m_x1;
-    RefPtr<SVGAnimatedLength> m_y1;
-    RefPtr<SVGAnimatedLength> m_x2;
-    RefPtr<SVGAnimatedLength> m_y2;
+    RefPtrWillBeMember<SVGAnimatedLength> m_x1;
+    RefPtrWillBeMember<SVGAnimatedLength> m_y1;
+    RefPtrWillBeMember<SVGAnimatedLength> m_x2;
+    RefPtrWillBeMember<SVGAnimatedLength> m_y2;
 };
 
 } // namespace blink
 
 #endif // SVGLinearGradientElement_h