Move RenderSVGResource into the inheritance hierarchy

Source/core/rendering/svg/RenderSVGResourceGradient.cpp

Index: Source/core/rendering/svg/RenderSVGResourceGradient.cpp
diff --git a/Source/core/rendering/svg/RenderSVGResourceGradient.cpp b/Source/core/rendering/svg/RenderSVGResourceGradient.cpp
index ca7a8b8a0f665e484d0e6b73b3c2f300e329308c..568e4f9cb44d69f2e9c732071df792efc348cb62 100644
--- a/Source/core/rendering/svg/RenderSVGResourceGradient.cpp
+++ b/Source/core/rendering/svg/RenderSVGResourceGradient.cpp
@@ -26,7 +26,7 @@
 namespace blink {
 
 RenderSVGResourceGradient::RenderSVGResourceGradient(SVGGradientElement* node)
-    : RenderSVGResourceContainer(node)
+    : RenderSVGResourcePaintServer(node)
     , m_shouldCollectGradientAttributes(true)
 {
 }
@@ -107,10 +107,7 @@ bool RenderSVGResourceGradient::isChildAllowed(RenderObject* child, RenderStyle*
     if (!child->isSVGResourceContainer())
         return false;
 
-    RenderSVGResourceContainer* resource = toRenderSVGResourceContainer(child);
-    return resource->resourceType() == PatternResourceType
-        || resource->resourceType() == LinearGradientResourceType
-        || resource->resourceType() == RadialGradientResourceType;
+    return toRenderSVGResourceContainer(child)->isSVGPaintServer();
 }
 
 void RenderSVGResourceGradient::addStops(GradientData* gradientData, const Vector<Gradient::ColorStop>& stops) const