Upgrade custom elements when inserting a node

third_party/WebKit/Source/core/dom/custom/CustomElementDefinition.cpp

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/dom/custom/CustomElementDefinition.h"
 
 #include "core/dom/Attr.h"
 #include "core/dom/ExceptionCode.h"
 #include "core/dom/custom/CEReactionsScope.h"
 #include "core/dom/custom/CustomElement.h"
@@ skipping 84 matching lines @@
     element->setCustomElementState(CustomElementState::Undefined);
     // 6.2.2. Enqueue a custom element upgrade reaction given result and
     // definition.
     enqueueUpgradeReaction(element);
     return element;
 }
 
 // https://html.spec.whatwg.org/multipage/scripting.html#concept-upgrade-an-element
 void CustomElementDefinition::upgrade(Element* element)
 {
+    DCHECK_EQ(element->getCustomElementState(), CustomElementState::Undefined);
+
     if (!m_observedAttributes.isEmpty())
         enqueueAttributeChangedCallbackForAllAttributes(element);
 
     if (element->inShadowIncludingDocument() && hasConnectedCallback())
         enqueueConnectedCallback(element);
 
     m_constructionStack.append(element);
     size_t depth = m_constructionStack.size();
 
     bool succeeded = runConstructor(element);
@@ skipping 56 matching lines @@
         element->synchronizeAttribute(name);
     for (const auto& attribute : element->attributesWithoutUpdate()) {
         if (hasAttributeChangedCallback(attribute.name())) {
             enqueueAttributeChangedCallback(element, attribute.name(),
                 nullAtom, attribute.value());
         }
     }
 }
 
 } // namespace blink