Ensure that every Document has a single, distinct template content ownerDocument

Source/core/dom/ContainerNode.cpp

Index: Source/core/dom/ContainerNode.cpp
diff --git a/Source/core/dom/ContainerNode.cpp b/Source/core/dom/ContainerNode.cpp
index f8f1f2db805bec9e07575faff72f3de1e488f389..2f4f605344b9795075420d50c02a4fff80932772 100644
--- a/Source/core/dom/ContainerNode.cpp
+++ b/Source/core/dom/ContainerNode.cpp
@@ -112,7 +112,7 @@ bool ContainerNode::isChildTypeAllowed(const Node& child) const
 
 bool ContainerNode::containsConsideringHostElements(const Node& newChild) const
 {
-    if (isInShadowTree() || document() == document().templateDocument())
+    if (isInShadowTree() || document().isTemplateDocument())
         return newChild.containsIncludingHostElements(*this);
     return newChild.contains(this);
 }