Introduce toSVGFontFaceElement, and use it

Source/core/css/CSSFontFaceSource.cpp

 /*
  * Copyright (C) 2007, 2008, 2010, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 126 matching lines @@
                 }
 
                 if (!m_externalSVGFontElement)
                     return 0;
 
                 SVGFontFaceElement* fontFaceElement = 0;
 
                 // Select first <font-face> child
                 for (Node* fontChild = m_externalSVGFontElement->firstChild(); fontChild; fontChild = fontChild->nextSibling()) {
                     if (fontChild->hasTagName(SVGNames::font_faceTag)) {
-                        fontFaceElement = static_cast<SVGFontFaceElement*>(fontChild);
+                        fontFaceElement = toSVGFontFaceElement(fontChild);
                         break;
                     }
                 }
 
                 if (fontFaceElement) {
                     if (!m_svgFontFaceElement) {
                         // We're created using a CSS @font-face rule, that means we're not associated with a SVGFontFaceElement.
                         // Use the imported <font-face> tag as referencing font-face element for these cases.
                         m_svgFontFaceElement = fontFaceElement;
                     }
@@ skipping 102 matching lines @@
     if (size < 50 * 1024)
         return "WebFont.LoadTime.1.10KBTo50KB";
     if (size < 100 * 1024)
         return "WebFont.LoadTime.2.50KBTo100KB";
     if (size < 1024 * 1024)
         return "WebFont.LoadTime.3.100KBTo1MB";
     return "WebFont.LoadTime.4.Over1MB";
 }
 
 }