Fix some SVGFonts compilation errors

Source/core/svg/SVGDocumentExtensions.cpp

 /*
  * Copyright (C) 2006 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2007 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.
  *
@@ skipping 462 matching lines @@
 SVGSVGElement* SVGDocumentExtensions::rootElement() const
 {
     ASSERT(m_document);
     return rootElement(*m_document);
 }
 
 void SVGDocumentExtensions::trace(Visitor* visitor)
 {
     visitor->trace(m_document);
     visitor->trace(m_timeContainers);
+#if ENABLE(SVG_FONTS)
     visitor->trace(m_svgFontFaceElements);
     visitor->trace(m_pendingSVGFontFaceElementsForRemoval);
+#endif
     visitor->trace(m_elementDependencies);
     visitor->trace(m_relativeLengthSVGRoots);
 }
 
 }