[CSS Regions] Elements in a region should be assignable to a named flow

Source/core/svg/SVGElement.cpp

Index: Source/core/svg/SVGElement.cpp
diff --git a/Source/core/svg/SVGElement.cpp b/Source/core/svg/SVGElement.cpp
index c2519cfeea8af7f149f95dde49af1cbe1bf8336f..84d0d0886a0a7f7be92db6587ab513c63fc76704 100644
--- a/Source/core/svg/SVGElement.cpp
+++ b/Source/core/svg/SVGElement.cpp
@@ -457,6 +457,12 @@ static bool hasLoadListener(Element* element)
     return false;
 }
 
+bool SVGElement::moveToFlowThreadIsNeeded(RefPtr<RenderStyle>& cachedStyle)
+{
+    // Allow only svg root elements to be directly collected by a render flow thread.
+    return parentNode() && !parentNode()->isSVGElement() && hasTagName(SVGNames::svgTag) && Element::moveToFlowThreadIsNeeded(cachedStyle);
+}
+
 void SVGElement::sendSVGLoadEventIfPossible(bool sendParentLoadEvents)
 {
     RefPtr<SVGElement> currentTarget = this;