Add toSVGFEFuncR|G|B|AElement() fuctions, and use them.

Source/core/svg/SVGFEFuncRElement.h

Index: Source/core/svg/SVGFEFuncRElement.h
diff --git a/Source/core/svg/SVGFEFuncRElement.h b/Source/core/svg/SVGFEFuncRElement.h
index 8b76e467bd64dd62494cda6c5720266e688232f9..4822a0b20bc17ae052acf08feff89ee4df9976c9 100644
--- a/Source/core/svg/SVGFEFuncRElement.h
+++ b/Source/core/svg/SVGFEFuncRElement.h
@@ -21,6 +21,7 @@
 #ifndef SVGFEFuncRElement_h
 #define SVGFEFuncRElement_h
 
+#include "SVGNames.h"
 #include "core/svg/SVGComponentTransferFunctionElement.h"
 
 namespace WebCore {
@@ -33,6 +34,12 @@ private:
     SVGFEFuncRElement(const QualifiedName&, Document&);
 };
 
+inline SVGFEFuncRElement* toSVGFEFuncRElement(Node* node)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!node || node->hasTagName(SVGNames::feFuncRTag));
+    return static_cast<SVGFEFuncRElement*>(node);
+}
+
 } // namespace WebCore
 
 #endif