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

third_party/WebKit/Source/core/html/HTMLButtonElement.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, 2010 Apple Inc. All rights reserved.
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2007 Samuel Weinig (sam@webkit.org)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 83 matching lines @@
 void HTMLButtonElement::parseAttribute(const QualifiedName& name, const AtomicString& oldValue, const AtomicString& value)
 {
     if (name == typeAttr) {
         if (equalIgnoringCase(value, "reset"))
             m_type = RESET;
         else if (equalIgnoringCase(value, "button"))
             m_type = BUTTON;
         else
             m_type = SUBMIT;
         setNeedsWillValidateCheck();
+        if (formOwner() && inDocument())
+            formOwner()->invalidateDefaultButtonStyle();
     } else {
         if (name == formactionAttr)
             logUpdateAttributeIfIsolatedWorldAndInDocument("button", formactionAttr, oldValue, value);
         HTMLFormControlElement::parseAttribute(name, oldValue, value);
     }
 }
 
 void HTMLButtonElement::defaultEventHandler(Event* event)
 {
     if (event->type() == EventTypeNames::DOMActivate && !isDisabledFormControl()) {
@@ skipping 99 matching lines @@
 }
 
 Node::InsertionNotificationRequest HTMLButtonElement::insertedInto(ContainerNode* insertionPoint)
 {
     InsertionNotificationRequest request = HTMLFormControlElement::insertedInto(insertionPoint);
     logAddElementIfIsolatedWorldAndInDocument("button", typeAttr, formmethodAttr, formactionAttr);
     return request;
 }
 
 } // namespace blink