Add toSVGCircleElement(), and use it

Source/core/svg/SVGCircleElement.h

Index: Source/core/svg/SVGCircleElement.h
diff --git a/Source/core/svg/SVGCircleElement.h b/Source/core/svg/SVGCircleElement.h
index 25b5d88f912224eef99a34f101a6f6effdf56cbc..99dc6421aa13cc62c67359fc19ea57117a44ce72 100644
--- a/Source/core/svg/SVGCircleElement.h
+++ b/Source/core/svg/SVGCircleElement.h
@@ -21,6 +21,7 @@
 #ifndef SVGCircleElement_h
 #define SVGCircleElement_h
 
+#include "SVGNames.h"
 #include "core/svg/SVGAnimatedBoolean.h"
 #include "core/svg/SVGAnimatedLength.h"
 #include "core/svg/SVGExternalResourcesRequired.h"
@@ -55,6 +56,12 @@ private:
     END_DECLARE_ANIMATED_PROPERTIES
 };
 
+inline SVGCircleElement* toSVGCircleElement(Node* node)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!node || node->hasTagName(SVGNames::circleTag));
+    return static_cast<SVGCircleElement*>(node);
+}
+
 } // namespace WebCore
 
 #endif // SVGCircleElement_h