Recursively defining custom elements should not lead to redefinition

third_party/WebKit/Source/core/dom/custom/CustomElementDefinitionBuilder.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 CustomElementDefinitionBuilder_h
 #define CustomElementDefinitionBuilder_h
 
 #include "core/CoreExport.h"
 #include "wtf/Allocator.h"
 #include "wtf/Noncopyable.h"
 
 namespace blink {
 
 class CustomElementDefinition;
 class CustomElementDescriptor;
 class CustomElementsRegistry;
 class ExceptionState;
 class ScriptState;
 class ScriptValue;
 
 // Implement CustomElementDefinitionBuilder to provide
 // technology-specific steps for CustomElementsRegistry.define.
 // https://html.spec.whatwg.org/multipage/scripting.html#dom-customelementsregistry-define
 class CORE_EXPORT CustomElementDefinitionBuilder {
     STACK_ALLOCATED();
     WTF_MAKE_NONCOPYABLE(CustomElementDefinitionBuilder);
 public:
-    CustomElementDefinitionBuilder() { }
+    CustomElementDefinitionBuilder() = default;
+    virtual ~CustomElementDefinitionBuilder() = default;
 
     // This API necessarily sounds JavaScript specific; this implements
     // some steps of the CustomElementsRegistry.define process, which
     // are defined in terms of JavaScript.
 
     // Check the constructor is valid. Return false if processing
     // should not proceed.
     virtual bool checkConstructorIntrinsics() = 0;
 
     // Check the constructor is not already registered in the calling
     // registry. Return false if processing should not proceed.
     virtual bool checkConstructorNotRegistered() = 0;
 
     // Checking the prototype may destroy the window. Return false if
     // processing should not proceed.
     virtual bool checkPrototype() = 0;
 
     // Produce the definition. This must produce a definition.
     virtual CustomElementDefinition* build(const CustomElementDescriptor&) = 0;
 };
 
 } // namespace blink
 
 #endif // CustomElementDefinitionBuilder_h