Upgrade elements that are created before a custom element definition is registered

Source/core/dom/CustomElementDefinition.h

Index: Source/core/dom/CustomElementDefinition.h
diff --git a/Source/core/dom/CustomElementDefinition.h b/Source/core/dom/CustomElementDefinition.h
index 644f6aa6c06f0d7e4ae38dba23bb715200b71b38..3df2e6c418df408d2763e82705b6bc818cae4f22 100644
--- a/Source/core/dom/CustomElementDefinition.h
+++ b/Source/core/dom/CustomElementDefinition.h
@@ -47,6 +47,11 @@ public:
 
     virtual ~CustomElementDefinition() {}
 
+    enum CustomElementKind {
+        CustomTag,
+        TypeExtension
+    };
+
     // This specifies whether the custom element is in the HTML or SVG
     // namespace.
     const AtomicString& namespaceURI() const { return m_tag.namespaceURI(); }
@@ -64,6 +69,7 @@ public:
     // name. This does not have a prefix.
     const QualifiedName& tagQName() const { return m_tag; }
 
+    CustomElementKind kind() const { return isTypeExtension() ? TypeExtension : CustomTag; }
     bool isTypeExtension() const { return type() != name(); }
 
     const ScriptValue& prototype() { return m_prototype; }