Remove support for the externalResourcesRequired attribute.

Source/core/svg/SVGImageElement.h

Index: Source/core/svg/SVGImageElement.h
diff --git a/Source/core/svg/SVGImageElement.h b/Source/core/svg/SVGImageElement.h
index c58bde73ab83bff7681ae8cd707e937d5a2b6acc..c131ee7c565468a947f09b0c43afe7a2cf7a29cb 100644
--- a/Source/core/svg/SVGImageElement.h
+++ b/Source/core/svg/SVGImageElement.h
@@ -25,7 +25,6 @@
 #include "core/svg/SVGAnimatedBoolean.h"
 #include "core/svg/SVGAnimatedLength.h"
 #include "core/svg/SVGAnimatedPreserveAspectRatio.h"
-#include "core/svg/SVGExternalResourcesRequired.h"
 #include "core/svg/SVGGraphicsElement.h"
 #include "core/svg/SVGImageLoader.h"
 #include "core/svg/SVGURIReference.h"
@@ -33,7 +32,6 @@
 namespace WebCore {
 
 class SVGImageElement FINAL : public SVGGraphicsElement,
-                              public SVGExternalResourcesRequired,
                               public SVGURIReference {
 public:
     static PassRefPtr<SVGImageElement> create(const QualifiedName&, Document&);
@@ -72,7 +70,6 @@ private:
         DECLARE_ANIMATED_LENGTH(Height, height)
         DECLARE_ANIMATED_PRESERVEASPECTRATIO(PreserveAspectRatio, preserveAspectRatio)
         DECLARE_ANIMATED_STRING(Href, href)
-        DECLARE_ANIMATED_BOOLEAN(ExternalResourcesRequired, externalResourcesRequired)
     END_DECLARE_ANIMATED_PROPERTIES
 
     SVGImageLoader m_imageLoader;