Introduce DEFINE_CUSTOM_FONT_DATA_TYPE_CASTS, and use it

Source/core/rendering/svg/SVGTextRunRenderingContext.cpp

 /*
  * Copyright (C) 2007, 2008 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) Research In Motion Limited 2010-2011. All rights reserved.
  *
  * 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,
@@ skipping 25 matching lines @@
 
 namespace blink {
 
 static inline const SVGFontData* svgFontAndFontFaceElementForFontData(const SimpleFontData* fontData, SVGFontFaceElement*& fontFace, SVGFontElement*& font)
 {
     ASSERT(fontData);
     ASSERT(fontData->isCustomFont());
     ASSERT(fontData->isSVGFont());
 
     RefPtr<CustomFontData> customFontData = fontData->customFontData();
-    const SVGFontData* svgFontData = static_cast<const SVGFontData*>(customFontData.get());
+    const SVGFontData* svgFontData = toSVGFontData(customFontData);
 
     // FIXME crbug.com/359380 : The current editing impl references the font after the svg font nodes are removed.
     if (svgFontData->shouldSkipDrawing())
         return 0;
 
     fontFace = svgFontData->svgFontFaceElement();
     ASSERT(fontFace);
 
     font = fontFace->associatedFontElement();
     return svgFontData;
@@ skipping 188 matching lines @@
     // Restore original state of the SVG Font glyph table and the current font fallback list,
     // to assure the next lookup of the same glyph won't immediately return the fallback glyph.
     page->setGlyphDataForCharacter(character, glyphData.glyph, originalFontData);
     ASSERT(fallbackGlyphData.fontData);
     return fallbackGlyphData;
 }
 
 }
 
 #endif