Clean up static_cast<SVGFooElement*> by using toSVGFoo()

Source/core/svg/SVGFontData.cpp

Index: Source/core/svg/SVGFontData.cpp
diff --git a/Source/core/svg/SVGFontData.cpp b/Source/core/svg/SVGFontData.cpp
index 3b3ea8f594fd046f0ad46fb2eb9c55ac2dc52d24..22f11eb04e8032dc4941cafd887835d8f1882482 100644
--- a/Source/core/svg/SVGFontData.cpp
+++ b/Source/core/svg/SVGFontData.cpp
@@ -176,8 +176,7 @@ bool SVGFontData::applySVGGlyphSelection(WidthIterator& iterator, GlyphData& gly
             language = parentRenderObjectElement->getAttribute(XMLNames::langAttr);
 
             if (parentRenderObjectElement->hasTagName(SVGNames::altGlyphTag)) {
-                SVGAltGlyphElement* altGlyph = static_cast<SVGAltGlyphElement*>(parentRenderObjectElement);
-                if (!altGlyph->hasValidGlyphElements(altGlyphNames))
+                if (!toSVGAltGlyphElement(parentRenderObjectElement)->hasValidGlyphElements(altGlyphNames))
                     altGlyphNames.clear();
             }
         }