Fix update of validity cache value, so that it reflects the correct state of any FormControlElement.

Source/core/html/HTMLTextAreaElement.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, 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 102 matching lines @@
     virtual bool hasCustomFocusLogic() const OVERRIDE;
     virtual bool shouldShowFocusRingOnMouseFocus() const OVERRIDE;
     virtual bool isKeyboardFocusable() const OVERRIDE;
     virtual void updateFocusAppearance(bool restorePreviousSelection) OVERRIDE;
 
     virtual void accessKeyAction(bool sendMouseEvents) OVERRIDE;
 
     virtual bool matchesReadOnlyPseudoClass() const OVERRIDE;
     virtual bool matchesReadWritePseudoClass() const OVERRIDE;
 
+    virtual void detach(const AttachContext&) OVERRIDE;
+
     bool valueMissing(const String& value) const { return isRequiredFormControl() && !isDisabledOrReadOnly() && value.isEmpty(); }
     bool tooLong(const String&, NeedsToCheckDirtyFlag) const;
 
     int m_rows;
     int m_cols;
     WrapMethod m_wrap;
     mutable String m_value;
     mutable bool m_isDirty;
     bool m_valueIsUpToDate;
     String m_suggestedValue;
 };
 
 } //namespace
 
 #endif