Add DCHECKs for catching inconsistent custom element state

third_party/WebKit/Source/core/html/parser/HTMLConstructionSite.cpp

 /*
  * Copyright (C) 2010 Google, Inc. All Rights Reserved.
  * Copyright (C) 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 836 matching lines @@
         // "9. If will execute script is true, then ..." etc. The
         // CEReactionsScope and ScriptNestingLevelIncrementer
         // destructors implement steps 9.1-4.
     } else {
         // FIXME: This can't use
         // HTMLConstructionSite::createElement because we have to
         // pass the current form element. We should rework form
         // association to occur after construction to allow better
         // code sharing here.
         element = HTMLElementFactory::createHTMLElement(token->name(), document, form, getCreateElementFlags());
+        // Definition for the created element does not exist here and
+        // it cannot be custom or failed.
+        DCHECK_NE(element->getCustomElementState(), CustomElementState::Custom);
+        DCHECK_NE(element->getCustomElementState(), CustomElementState::Failed);
 
         // "8. Append each attribute in the given token to element."
         setAttributes(element, token, m_parserContentPolicy);
     }
 
     // TODO(dominicc): Implement steps 10-12 when customized built-in
     // elements are implemented.
 
     return element;
 }
@@ skipping 112 matching lines @@
     queueTask(task);
 }
 
 DEFINE_TRACE(HTMLConstructionSite::PendingText)
 {
     visitor->trace(parent);
     visitor->trace(nextChild);
 }
 
 } // namespace blink