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

Source/core/svg/SVGFEFuncBElement.h

Index: Source/core/svg/SVGFEFuncBElement.h
diff --git a/Source/core/svg/SVGFEFuncBElement.h b/Source/core/svg/SVGFEFuncBElement.h
index 3c0fbceaa325f8f119f967a1b281e53578f71adc..6bf582e591238fd23d18686bae5918284bf98241 100644
--- a/Source/core/svg/SVGFEFuncBElement.h
+++ b/Source/core/svg/SVGFEFuncBElement.h
@@ -21,6 +21,7 @@
 #ifndef SVGFEFuncBElement_h
 #define SVGFEFuncBElement_h
 
+#include "SVGNames.h"
 #include "core/svg/SVGComponentTransferFunctionElement.h"
 
 namespace WebCore {
@@ -33,6 +34,12 @@ private:
     SVGFEFuncBElement(const QualifiedName&, Document&);
 };
 
+inline SVGFEFuncBElement* toSVGFEFuncBElement(Node* node)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!node || node->hasTagName(SVGNames::feFuncBTag));
+    return static_cast<SVGFEFuncBElement*>(node);
+}
+
 } // namespace WebCore
 
 #endif