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

Source/core/svg/SVGFEFuncGElement.h

Index: Source/core/svg/SVGFEFuncGElement.h
diff --git a/Source/core/svg/SVGFEFuncGElement.h b/Source/core/svg/SVGFEFuncGElement.h
index 3121aeaae4cc417ff70b0c4dab850a044e63a328..5b29bdc0ccf5282e621ce4d3c868f66f90aba6bd 100644
--- a/Source/core/svg/SVGFEFuncGElement.h
+++ b/Source/core/svg/SVGFEFuncGElement.h
@@ -21,6 +21,7 @@
 #ifndef SVGFEFuncGElement_h
 #define SVGFEFuncGElement_h
 
+#include "SVGNames.h"
 #include "core/svg/SVGComponentTransferFunctionElement.h"
 
 namespace WebCore {
@@ -33,6 +34,12 @@ private:
     SVGFEFuncGElement(const QualifiedName&, Document&);
 };
 
+inline SVGFEFuncGElement* toSVGFEFuncGElement(Node* node)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!node || node->hasTagName(SVGNames::feFuncGTag));
+    return static_cast<SVGFEFuncGElement*>(node);
+}
+
 } // namespace WebCore
 
 #endif