Use isSVG*Element() helpers more in SVG code (Part 2)

Source/core/svg/SVGGlyphElement.cpp

 /*
  * Copyright (C) 2007 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2007, 2008 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2008 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 26 matching lines @@
 }
 
 PassRefPtr<SVGGlyphElement> SVGGlyphElement::create(Document& document)
 {
     return adoptRef(new SVGGlyphElement(document));
 }
 
 void SVGGlyphElement::invalidateGlyphCache()
 {
     ContainerNode* fontNode = parentNode();
-    if (fontNode && fontNode->hasTagName(SVGNames::fontTag))
-        toSVGFontElement(fontNode)->invalidateGlyphCache();
+    if (isSVGFontElement(fontNode))
+        toSVGFontElement(*fontNode).invalidateGlyphCache();
 }
 
 void SVGGlyphElement::parseAttribute(const QualifiedName& name, const AtomicString& value)
 {
     if (name == SVGNames::dAttr)
         invalidateGlyphCache();
     else
         SVGElement::parseAttribute(name, value);
 }
 
@@ skipping 97 matching lines @@
     String language = fastGetAttribute(SVGNames::langAttr);
     if (!language.isEmpty())
         identifier.languages = parseDelimitedString(language, ',');
 
     return identifier;
 }
 
 }
 
 #endif // ENABLE(SVG_FONTS)