Introduce toSVGLineElement(), and use it

Source/core/svg/SVGLineElement.h

Index: Source/core/svg/SVGLineElement.h
diff --git a/Source/core/svg/SVGLineElement.h b/Source/core/svg/SVGLineElement.h
index f90960ad1012a9d1cf7ec91b68fccf3ef7fb7803..c1e8a5143d9a588b480b99b57ecb30b7143e6240 100644
--- a/Source/core/svg/SVGLineElement.h
+++ b/Source/core/svg/SVGLineElement.h
@@ -21,6 +21,7 @@
 #ifndef SVGLineElement_h
 #define SVGLineElement_h
 
+#include "SVGNames.h"
 #include "core/svg/SVGAnimatedBoolean.h"
 #include "core/svg/SVGAnimatedLength.h"
 #include "core/svg/SVGExternalResourcesRequired.h"
@@ -56,6 +57,12 @@ private:
     END_DECLARE_ANIMATED_PROPERTIES
 };
 
+inline SVGLineElement* toSVGLineElement(Element* element)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!element || element->hasTagName(SVGNames::lineTag));
+    return static_cast<SVGLineElement*>(element);
+}
+
 } // namespace WebCore
 
 #endif