Invalidate :default pseudo classes when a default button is added or removed.

third_party/WebKit/Source/core/html/HTMLFormElement.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 99 matching lines @@
 
     DEFINE_ATTRIBUTE_EVENT_LISTENER(autocomplete);
     DEFINE_ATTRIBUTE_EVENT_LISTENER(autocompleteerror);
 
     RadioButtonGroupScope& radioButtonGroupScope() { return m_radioButtonGroupScope; }
 
     const FormAssociatedElement::List& associatedElements() const;
     const WillBeHeapVector<RawPtrWillBeMember<HTMLImageElement>>& imageElements();
 
     void anonymousNamedGetter(const AtomicString& name, RadioNodeListOrElement&);
+    void invalidateDefaultButtonStyle() const;
 
 private:
     explicit HTMLFormElement(Document&);
 
     bool layoutObjectIsNeeded(const ComputedStyle&) override;
     InsertionNotificationRequest insertedInto(ContainerNode*) override;
     void removedFrom(ContainerNode*) override;
     void finishParsingChildren() override;
 
     void handleLocalEvents(Event&) override;
@@ skipping 36 matching lines @@
     // Do not access m_associatedElements directly. Use associatedElements() instead.
     FormAssociatedElement::List m_associatedElements;
     // Do not access m_imageElements directly. Use imageElements() instead.
     WillBeHeapVector<RawPtrWillBeMember<HTMLImageElement>> m_imageElements;
 #if !ENABLE(OILPAN)
     WeakPtrFactory<HTMLFormElement> m_weakPtrFactory;
 #endif
     bool m_associatedElementsAreDirty : 1;
     bool m_imageElementsAreDirty : 1;
     bool m_hasElementsAssociatedByParser : 1;
+    bool m_hasElementsAssociatedByFormAttribute : 1;
     bool m_didFinishParsingChildren : 1;
 
     bool m_wasUserSubmitted : 1;
     bool m_isSubmittingOrInUserJSSubmitEvent : 1;
     bool m_shouldSubmit : 1;
 
     bool m_isInResetFunction : 1;
 
     bool m_wasDemoted : 1;
 
     OwnPtrWillBeMember<GenericEventQueue> m_pendingAutocompleteEventsQueue;
 };
 
 } // namespace blink
 
 #endif // HTMLFormElement_h