Use new is*Element() helper functions more in core/ code

Source/core/fetch/FontResource.cpp

 /*
  * Copyright (C) 2006, 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Torch Mobile, Inc.
  *
  * 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
@@ skipping 125 matching lines @@
     if (!collection)
         return 0;
 
     unsigned collectionLength = collection->length();
     if (!collectionLength)
         return 0;
 
 #ifndef NDEBUG
     for (unsigned i = 0; i < collectionLength; ++i) {
         ASSERT(collection->item(i));
-        ASSERT(collection->item(i)->hasTagName(SVGNames::fontTag));
+        ASSERT(isSVGFontElement(collection->item(i)));
     }
 #endif
 
     if (fontName.isEmpty())
         return toSVGFontElement(collection->item(0));
 
     for (unsigned i = 0; i < collectionLength; ++i) {
         SVGFontElement* element = toSVGFontElement(collection->item(i));
         if (element->getIdAttribute() == fontName)
             return element;
@@ skipping 26 matching lines @@
 
 void FontResource::checkNotify()
 {
     m_fontLoadWaitLimitTimer.stop();
     ResourceClientWalker<FontResourceClient> w(m_clients);
     while (FontResourceClient* c = w.next())
         c->fontLoaded(this);
 }
 
 }