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

Source/core/svg/SVGFEFuncAElement.h

Index: Source/core/svg/SVGFEFuncAElement.h
diff --git a/Source/core/svg/SVGFEFuncAElement.h b/Source/core/svg/SVGFEFuncAElement.h
index db63a153c57c1a93332606f51219b1e23794c24c..7f6cfdc6e613b3152b9382d0b8cc676d158928b6 100644
--- a/Source/core/svg/SVGFEFuncAElement.h
+++ b/Source/core/svg/SVGFEFuncAElement.h
@@ -21,6 +21,7 @@
 #ifndef SVGFEFuncAElement_h
 #define SVGFEFuncAElement_h
 
+#include "SVGNames.h"
 #include "core/svg/SVGComponentTransferFunctionElement.h"
 
 namespace WebCore {
@@ -33,6 +34,12 @@ private:
     SVGFEFuncAElement(const QualifiedName&, Document&);
 };
 
+inline SVGFEFuncAElement* toSVGFEFuncAElement(Node* node)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!node || node->hasTagName(SVGNames::feFuncATag));
+    return static_cast<SVGFEFuncAElement*>(node);
+}
+
 } // namespace WebCore
 
 #endif