Introduce toSVGMPathElement(), and use it

Source/core/svg/SVGMPathElement.h

Index: Source/core/svg/SVGMPathElement.h
diff --git a/Source/core/svg/SVGMPathElement.h b/Source/core/svg/SVGMPathElement.h
index c8af628fddcf341b58ef27e88bfc9f1203be6387..bd412a867c0f210c6994d13c240b87ea29151ce5 100644
--- a/Source/core/svg/SVGMPathElement.h
+++ b/Source/core/svg/SVGMPathElement.h
@@ -20,6 +20,7 @@
 #ifndef SVGMPathElement_h
 #define SVGMPathElement_h
 
+#include "SVGNames.h"
 #include "core/svg/SVGAnimatedBoolean.h"
 #include "core/svg/SVGAnimatedString.h"
 #include "core/svg/SVGElement.h"
@@ -63,6 +64,12 @@ private:
     END_DECLARE_ANIMATED_PROPERTIES
 };
 
+inline SVGMPathElement* toSVGMPathElement(Node* node)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!node || node->hasTagName(SVGNames::mpathTag));
+    return static_cast<SVGMPathElement*>(node);
+}
+
 } // namespace WebCore
 
 #endif // SVGMPathElement_h