Add toSVGFontFaceUri|NameElement(), and use them.

Source/core/svg/SVGFontFaceUriElement.h

Index: Source/core/svg/SVGFontFaceUriElement.h
diff --git a/Source/core/svg/SVGFontFaceUriElement.h b/Source/core/svg/SVGFontFaceUriElement.h
index fb4f8c80345cb5d034e73d6229ed659cba2bcc53..8a3f84eedd5cee50d59a4f303ae8120878b77388 100644
--- a/Source/core/svg/SVGFontFaceUriElement.h
+++ b/Source/core/svg/SVGFontFaceUriElement.h
@@ -21,6 +21,7 @@
 #define SVGFontFaceUriElement_h
 
 #if ENABLE(SVG_FONTS)
+#include "SVGNames.h"
 #include "core/fetch/FontResource.h"
 #include "core/fetch/ResourcePtr.h"
 #include "core/svg/SVGElement.h"
@@ -51,6 +52,12 @@ private:
     ResourcePtr<FontResource> m_resource;
 };
 
+inline SVGFontFaceUriElement* toSVGFontFaceUriElement(Node* node)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!node || node->hasTagName(SVGNames::font_face_uriTag));
+    return static_cast<SVGFontFaceUriElement*>(node);
+}
+
 } // namespace WebCore
 
 #endif // ENABLE(SVG_FONTS)