Oilpan: add SVGRemoteFontFaceSource::trace().

Source/core/svg/SVGRemoteFontFaceSource.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef SVGRemoteFontFaceSource_h
 #define SVGRemoteFontFaceSource_h
 
 #if ENABLE(SVG_FONTS)
 
 #include "core/css/RemoteFontFaceSource.h"
 #include "platform/heap/Handle.h"
 
 namespace WebCore {
 
 class SVGFontElement;
 
 class SVGRemoteFontFaceSource : public RemoteFontFaceSource {
 public:
     SVGRemoteFontFaceSource(const String& uri, FontResource*, PassRefPtrWillBeRawPtr<FontLoader>);
     ~SVGRemoteFontFaceSource();
     virtual bool isSVGFontFaceSource() const OVERRIDE { return true; }
     virtual bool ensureFontData() OVERRIDE;
 
+    virtual void trace(Visitor*) OVERRIDE;
+
 private:
     virtual PassRefPtr<SimpleFontData> createFontData(const FontDescription&) OVERRIDE;
 
     String m_uri;
-    RefPtrWillBePersistent<SVGFontElement> m_externalSVGFontElement;
+    RefPtrWillBeMember<SVGFontElement> m_externalSVGFontElement;
 };
 
 } // namespace WebCore
 
 #endif // ENABLE(SVG_FONTS)
 #endif