Recursively defining custom elements should not lead to redefinition

third_party/WebKit/Source/core/dom/custom/CustomElementsRegistry.h

 // 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.
 
 #ifndef CustomElementsRegistry_h
 #define CustomElementsRegistry_h
 
 #include "bindings/core/v8/ScriptWrappable.h"
 #include "core/CoreExport.h"
 #include "platform/heap/Handle.h"
+#include "wtf/HashSet.h"
 #include "wtf/Noncopyable.h"
 #include "wtf/text/AtomicString.h"
 #include "wtf/text/AtomicStringHash.h"
 
 namespace blink {
 
 class CustomElementDefinition;
 class CustomElementDefinitionBuilder;
 class ElementRegistrationOptions;
 class ExceptionState;
@@ skipping 29 matching lines @@
     }
 
     CustomElementDefinition* definitionForName(const AtomicString& name) const;
 
     DECLARE_TRACE();
 
 private:
     CustomElementsRegistry(const V0CustomElementRegistrationContext*);
     bool v0NameIsDefined(const AtomicString&) const;
 
+    class NameIsBeingDefined;
+
+    HashSet<AtomicString> m_namesBeingDefined;
     using DefinitionMap =
         HeapHashMap<AtomicString, Member<CustomElementDefinition>>;
     DefinitionMap m_definitions;
 
     Member<const V0CustomElementRegistrationContext> m_v0;
 };
 
 } // namespace blink
 
 #endif // CustomElementsRegistry_h