Use isSVG*Element() helpers more in SVG code (Part 1)

Source/core/svg/SVGAltGlyphItemElement.cpp

Index: Source/core/svg/SVGAltGlyphItemElement.cpp
diff --git a/Source/core/svg/SVGAltGlyphItemElement.cpp b/Source/core/svg/SVGAltGlyphItemElement.cpp
index abe9e8d6785b3800f4f1e245bdfe484535c46e49..94c5fafcfbe705665a9920e9a7b3411d9c22795d 100644
--- a/Source/core/svg/SVGAltGlyphItemElement.cpp
+++ b/Source/core/svg/SVGAltGlyphItemElement.cpp
@@ -22,6 +22,7 @@
 #if ENABLE(SVG_FONTS)
 #include "core/svg/SVGAltGlyphItemElement.h"
 
+#include "core/dom/ElementTraversal.h"
 #include "core/svg/SVGGlyphRefElement.h"
 
 namespace WebCore {
@@ -47,15 +48,13 @@ bool SVGAltGlyphItemElement::hasValidGlyphElements(Vector<AtomicString>& glyphNa
     //
     // Here we fill glyphNames and return true only if all referenced glyphs are valid and
     // there is at least one glyph.
-    for (Node* child = firstChild(); child; child = child->nextSibling()) {
-        if (child->hasTagName(SVGNames::glyphRefTag)) {
-            AtomicString referredGlyphName;
-            if (toSVGGlyphRefElement(child)->hasValidGlyphElement(referredGlyphName))
-                glyphNames.append(referredGlyphName);
-            else {
-                glyphNames.clear();
-                return false;
-            }
+    for (SVGGlyphRefElement* glyph = Traversal<SVGGlyphRefElement>::firstChild(*this); glyph; glyph = Traversal<SVGGlyphRefElement>::nextSibling(*glyph)) {
+        AtomicString referredGlyphName;
+        if (glyph->hasValidGlyphElement(referredGlyphName)) {
+            glyphNames.append(referredGlyphName);
+        } else {
+            glyphNames.clear();
+            return false;
         }
     }
     return !glyphNames.isEmpty();