Remove support for the externalResourcesRequired attribute.

Source/core/svg/SVGMarkerElement.h

Index: Source/core/svg/SVGMarkerElement.h
diff --git a/Source/core/svg/SVGMarkerElement.h b/Source/core/svg/SVGMarkerElement.h
index da6b4654f8ff4652ed99dddba18227e41520824b..80c96d251932918e81d71da32fb32528f14fdcf1 100644
--- a/Source/core/svg/SVGMarkerElement.h
+++ b/Source/core/svg/SVGMarkerElement.h
@@ -29,7 +29,6 @@
 #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 {
@@ -95,7 +94,6 @@ struct SVGPropertyTraits<SVGMarkerOrientType> {
 };
 
 class SVGMarkerElement FINAL : public SVGElement,
-                               public SVGExternalResourcesRequired,
                                public SVGFitToViewBox {
 public:
     // Forward declare enumerations in the W3C naming scheme, for IDL generation.
@@ -157,7 +155,6 @@ private:
         DECLARE_ANIMATED_LENGTH(MarkerHeight, markerHeight)
         DECLARE_ANIMATED_ENUMERATION(MarkerUnits, markerUnits, SVGMarkerUnitsType)
         DECLARE_ANIMATED_ANGLE(OrientAngle, orientAngle)
-        DECLARE_ANIMATED_BOOLEAN(ExternalResourcesRequired, externalResourcesRequired)
         DECLARE_ANIMATED_RECT(ViewBox, viewBox)
         DECLARE_ANIMATED_PRESERVEASPECTRATIO(PreserveAspectRatio, preserveAspectRatio)
     END_DECLARE_ANIMATED_PROPERTIES