Add toSVGForeignObjectElement(), and use it.

Source/core/svg/SVGForeignObjectElement.h

Index: Source/core/svg/SVGForeignObjectElement.h
diff --git a/Source/core/svg/SVGForeignObjectElement.h b/Source/core/svg/SVGForeignObjectElement.h
index 48dcd3597c09be53bfbdac0418742ac49a3e9038..83018a89a72f419bde7233e70402ac0d60de5602 100644
--- a/Source/core/svg/SVGForeignObjectElement.h
+++ b/Source/core/svg/SVGForeignObjectElement.h
@@ -20,6 +20,7 @@
 #ifndef SVGForeignObjectElement_h
 #define SVGForeignObjectElement_h
 
+#include "SVGNames.h"
 #include "core/svg/SVGAnimatedBoolean.h"
 #include "core/svg/SVGAnimatedLength.h"
 #include "core/svg/SVGExternalResourcesRequired.h"
@@ -57,6 +58,12 @@ private:
     END_DECLARE_ANIMATED_PROPERTIES
 };
 
+inline SVGForeignObjectElement* toSVGForeignObjectElement(Node* node)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!node || node->hasTagName(SVGNames::foreignObjectTag));
+    return static_cast<SVGForeignObjectElement*>(node);
+}
+
 } // namespace WebCore
 
 #endif