Add toSVGFontFaceUri|NameElement(), and use them.

Source/core/svg/SVGFontFaceNameElement.h

Index: Source/core/svg/SVGFontFaceNameElement.h
diff --git a/Source/core/svg/SVGFontFaceNameElement.h b/Source/core/svg/SVGFontFaceNameElement.h
index 92cadec05066b74d1b50b66f9eb4b885d843e324..1339e4aa6183905938b2b6a021913be6aa138464 100644
--- a/Source/core/svg/SVGFontFaceNameElement.h
+++ b/Source/core/svg/SVGFontFaceNameElement.h
@@ -21,6 +21,7 @@
 #define SVGFontFaceNameElement_h
 
 #if ENABLE(SVG_FONTS)
+#include "SVGNames.h"
 #include "core/svg/SVGElement.h"
 
 namespace WebCore {
@@ -39,6 +40,12 @@ private:
     virtual bool rendererIsNeeded(const RenderStyle&) OVERRIDE { return false; }
 };
 
+inline SVGFontFaceNameElement* toSVGFontFaceNameElement(Node* node)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!node || node->hasTagName(SVGNames::font_face_nameTag));
+    return static_cast<SVGFontFaceNameElement*>(node);
+}
+
 } // namespace WebCore
 
 #endif // ENABLE(SVG_FONTS)