Dispatch change event for input type=checkbox when checked but value is null

Source/core/html/HTMLTextFormControlElement.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.
  * Copyright (C) 2009, 2010, 2011 Google 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
@@ skipping 92 matching lines @@
 
     void restoreCachedSelection();
 
     virtual void defaultEventHandler(Event*) OVERRIDE;
     virtual void subtreeHasChanged() = 0;
 
     void setLastChangeWasNotUserEdit() { m_lastChangeWasUserEdit = false; }
 
     String valueWithHardLineBreaks() const;
 
+    virtual bool shouldDispatchFormControlChangeEvent(String&, String&);
+
 private:
     int computeSelectionStart() const;
     int computeSelectionEnd() const;
     TextFieldSelectionDirection computeSelectionDirection() const;
 
     virtual void dispatchFocusEvent(Element* oldFocusedElement, FocusType) OVERRIDE FINAL;
     virtual void dispatchBlurEvent(Element* newFocusedElement) OVERRIDE FINAL;
 
     // Returns true if user-editable value is empty. Used to check placeholder visibility.
     virtual bool isEmptyValue() const = 0;
@@ skipping 17 matching lines @@
     return element.isTextFormControl();
 }
 
 DEFINE_HTMLELEMENT_TYPE_CASTS_WITH_FUNCTION(HTMLTextFormControlElement);
 
 HTMLTextFormControlElement* enclosingTextFormControl(const Position&);
 
 } // namespace
 
 #endif