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

third_party/WebKit/Source/core/html/HTMLFormControlElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007 Apple Inc. All rights reserved.
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  *
  * 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
@@ skipping 283 matching lines @@
     setNeedsWillValidateCheck();
     HTMLElement::removedFrom(insertionPoint);
     FormAssociatedElement::removedFrom(insertionPoint);
     document().removeFormAssociation(this);
 }
 
 void HTMLFormControlElement::willChangeForm()
 {
     FormAssociatedElement::willChangeForm();
     formOwnerSetNeedsValidityCheck();
+    if (formOwner() && canBeSuccessfulSubmitButton())
+        formOwner()->invalidateDefaultButtonStyle();
 }
 
 void HTMLFormControlElement::didChangeForm()
 {
     FormAssociatedElement::didChangeForm();
     formOwnerSetNeedsValidityCheck();
+    if (formOwner() && inDocument() && canBeSuccessfulSubmitButton())
+        formOwner()->invalidateDefaultButtonStyle();
 }
 
 void HTMLFormControlElement::formOwnerSetNeedsValidityCheck()
 {
     if (HTMLFormElement* form = formOwner()) {
         form->pseudoStateChanged(CSSSelector::PseudoValid);
         form->pseudoStateChanged(CSSSelector::PseudoInvalid);
     }
 }
 
@@ skipping 344 matching lines @@
         dispatchFormControlChangeEvent();
 }
 
 void HTMLFormControlElement::copyNonAttributePropertiesFromElement(const Element& source)
 {
     HTMLElement::copyNonAttributePropertiesFromElement(source);
     setNeedsValidityCheck();
 }
 
 } // namespace blink