[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 d5178e594a5bfebca2dd2587f9c84010c630d2d2..af503239c42b2386616574a446e9a61819c17b28 100644
--- a/Source/core/svg/SVGElement.cpp
+++ b/Source/core/svg/SVGElement.cpp
@@ -456,6 +456,12 @@ static bool hasLoadListener(Element* element)
     return false;
 }
 
+bool SVGElement::shouldMoveToFlowThread(RenderStyle* styleToUse) const
+{
+    // Allow only svg root elements to be directly collected by a render flow thread.
+    return parentNode() && !parentNode()->isSVGElement() && hasTagName(SVGNames::svgTag) && Element::shouldMoveToFlowThread(styleToUse);
+}
+
 void SVGElement::sendSVGLoadEventIfPossible(bool sendParentLoadEvents)
 {
     RefPtr<SVGElement> currentTarget = this;