Introduce toSVGRadialGradientElement(), and use it

Source/core/svg/SVGRadialGradientElement.h

Index: Source/core/svg/SVGRadialGradientElement.h
diff --git a/Source/core/svg/SVGRadialGradientElement.h b/Source/core/svg/SVGRadialGradientElement.h
index f70de31d776234df82f16499cf58d27c0cb164a0..20be5647b6dafd01460481edea69f237dad68f5a 100644
--- a/Source/core/svg/SVGRadialGradientElement.h
+++ b/Source/core/svg/SVGRadialGradientElement.h
@@ -21,6 +21,7 @@
 #ifndef SVGRadialGradientElement_h
 #define SVGRadialGradientElement_h
 
+#include "SVGNames.h"
 #include "core/svg/SVGAnimatedLength.h"
 #include "core/svg/SVGGradientElement.h"
 
@@ -55,6 +56,12 @@ private:
     END_DECLARE_ANIMATED_PROPERTIES
 };
 
+inline SVGRadialGradientElement* toSVGRadialGradientElement(Node* node)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!node || node->hasTagName(SVGNames::radialGradientTag));
+    return static_cast<SVGRadialGradientElement*>(node);
+}
+
 } // namespace WebCore
 
 #endif