Oilpan: add SVGRemoteFontFaceSource::trace().

Source/core/svg/SVGRemoteFontFaceSource.cpp

 // 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.
 
 #include "config.h"
 #if ENABLE(SVG_FONTS)
 #include "core/svg/SVGRemoteFontFaceSource.h"
 
 #include "SVGNames.h"
 #include "core/css/FontLoader.h"
@@ skipping 45 matching lines @@
     if (SVGFontFaceElement* fontFaceElement = Traversal<SVGFontFaceElement>::firstChild(*m_externalSVGFontElement)) {
         return SimpleFontData::create(
             SVGFontData::create(fontFaceElement),
             fontDescription.effectiveFontSize(),
             fontDescription.isSyntheticBold(),
             fontDescription.isSyntheticItalic());
     }
     return nullptr;
 }
 
+void SVGRemoteFontFaceSource::trace(Visitor* visitor)
+{
+    visitor->trace(m_externalSVGFontElement);
+    RemoteFontFaceSource::trace(visitor);
+}
+
 } // namespace WebCore
 
 #endif // ENABLE(SVG_FONTS)