Recursively defining custom elements should not lead to redefinition

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

Index: third_party/WebKit/Source/core/dom/custom/CustomElementsRegistry.h
diff --git a/third_party/WebKit/Source/core/dom/custom/CustomElementsRegistry.h b/third_party/WebKit/Source/core/dom/custom/CustomElementsRegistry.h
index da65a760ae6833e6924a8387d10a7884487647aa..f98bf839145a38dff95bfe074337573d37e8fec6 100644
--- a/third_party/WebKit/Source/core/dom/custom/CustomElementsRegistry.h
+++ b/third_party/WebKit/Source/core/dom/custom/CustomElementsRegistry.h
@@ -9,6 +9,7 @@
 #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"
@@ -27,13 +28,15 @@ class ScriptValue;
 class V0CustomElementRegistrationContext;
 
 class CORE_EXPORT CustomElementsRegistry final
-    : public GarbageCollected<CustomElementsRegistry>
+    : public GarbageCollectedFinalized<CustomElementsRegistry>
     , public ScriptWrappable {
     DEFINE_WRAPPERTYPEINFO();
     WTF_MAKE_NONCOPYABLE(CustomElementsRegistry);
 public:
     static CustomElementsRegistry* create(Document*);
 
+    virtual ~CustomElementsRegistry() = default;
+
     void define(
         ScriptState*,
         const AtomicString& name,
@@ -69,6 +72,9 @@ private:
         const CustomElementDescriptor&,
         HeapVector<Member<Element>>*);
 
+    class NameIsBeingDefined;
+
+    HashSet<AtomicString> m_namesBeingDefined;
     using DefinitionMap =
         HeapHashMap<AtomicString, Member<CustomElementDefinition>>;
     DefinitionMap m_definitions;