Remove support for the externalResourcesRequired attribute.

Source/core/svg/SVGSymbolElement.h

Index: Source/core/svg/SVGSymbolElement.h
diff --git a/Source/core/svg/SVGSymbolElement.h b/Source/core/svg/SVGSymbolElement.h
index 9d010de67c56f0916f5caaf8340dfebb0feff471..1eeb711b393e23b4895f945d6a7fc118ab0b412a 100644
--- a/Source/core/svg/SVGSymbolElement.h
+++ b/Source/core/svg/SVGSymbolElement.h
@@ -25,13 +25,11 @@
 #include "core/svg/SVGAnimatedPreserveAspectRatio.h"
 #include "core/svg/SVGAnimatedRect.h"
 #include "core/svg/SVGElement.h"
-#include "core/svg/SVGExternalResourcesRequired.h"
 #include "core/svg/SVGFitToViewBox.h"
 
 namespace WebCore {
 
 class SVGSymbolElement FINAL : public SVGElement,
-                               public SVGExternalResourcesRequired,
                                public SVGFitToViewBox {
 public:
     static PassRefPtr<SVGSymbolElement> create(const QualifiedName&, Document&);
@@ -50,7 +48,6 @@ private:
     virtual bool selfHasRelativeLengths() const;
 
     BEGIN_DECLARE_ANIMATED_PROPERTIES(SVGSymbolElement)
-        DECLARE_ANIMATED_BOOLEAN(ExternalResourcesRequired, externalResourcesRequired)
         DECLARE_ANIMATED_RECT(ViewBox, viewBox)
         DECLARE_ANIMATED_PRESERVEASPECTRATIO(PreserveAspectRatio, preserveAspectRatio)
     END_DECLARE_ANIMATED_PROPERTIES