Add toSVGTextPathElement(), and use it

Source/core/svg/SVGTextPathElement.h

Index: Source/core/svg/SVGTextPathElement.h
diff --git a/Source/core/svg/SVGTextPathElement.h b/Source/core/svg/SVGTextPathElement.h
index ab6bcb9881b682fd136d86db5de77ac26b77b45b..0ad3f96f238922a786a8fda9b31bde5b4441e4b0 100644
--- a/Source/core/svg/SVGTextPathElement.h
+++ b/Source/core/svg/SVGTextPathElement.h
@@ -20,8 +20,8 @@
 #ifndef SVGTextPathElement_h
 #define SVGTextPathElement_h
 
+#include "SVGNames.h"
 #include "core/svg/SVGTextContentElement.h"
-
 #include "core/svg/SVGURIReference.h"
 
 namespace WebCore {
@@ -140,6 +140,12 @@ private:
     END_DECLARE_ANIMATED_PROPERTIES
 };
 
+inline SVGTextPathElement* toSVGTextPathElement(Node* node)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!node || node->hasTagName(SVGNames::textPathTag));
+    return static_cast<SVGTextPathElement*>(node);
+}
+
 } // namespace WebCore
 
 #endif