Output Element defaultValue should be based on textContent

Source/core/html/HTMLOutputElement.cpp

 /*
  * Copyright (c) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 100 matching lines @@
 
 void HTMLOutputElement::setValue(const String& value)
 {
     // The value mode flag set to "value" when the value attribute is set.
     m_isDefaultValueMode = false;
     if (value == this->value())
         return;
     setTextContentInternal(value);
 }
 
-String HTMLOutputElement::defaultValue() const
+String HTMLOutputElement::defaultValue()
 {
+    if (m_isDefaultValueMode && m_defaultValue != value())
+        setDefaultValue(value());
     return m_defaultValue;
 }
 
 void HTMLOutputElement::setDefaultValue(const String& value)
 {
     if (m_defaultValue == value)
         return;
     m_defaultValue = value;
     // The spec requires the value attribute set to the default value
     // when the element's value mode flag to "default".
     if (m_isDefaultValueMode)
         setTextContentInternal(value);
 }
 
 void HTMLOutputElement::setTextContentInternal(const String& value)
 {
     ASSERT(!m_isSetTextContentInProgress);
     m_isSetTextContentInProgress = true;
     setTextContent(value);
 }
 
 } // namespace