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

Source/core/html/forms/InputType.h

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  * Copyright (C) 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2012 Samsung Electronics. 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
@@ skipping 202 matching lines @@
     // element is image. It returns 0 if the element is not image type.
     virtual unsigned height() const;
     virtual unsigned width() const;
 
     void dispatchSimulatedClickIfActive(KeyboardEvent*) const;
 
     // InputTypeView override
     virtual bool shouldSubmitImplicitly(Event*) OVERRIDE;
     virtual bool hasCustomFocusLogic() const OVERRIDE;
 
+    virtual bool shouldDispatchFormControlChangeEvent(String&, String&);
+
 protected:
     InputType(HTMLInputElement& element) : InputTypeView(element) { }
     Chrome* chrome() const;
     Locale& locale() const;
     Decimal parseToNumberOrNaN(const String&) const;
     void countUsageIfVisible(UseCounter::Feature) const;
 
     // Derive the step base, following the HTML algorithm steps.
     Decimal findStepBase(const Decimal&) const;
 
     StepRange createStepRange(AnyStepHandling, const Decimal& stepBaseDefault, const Decimal& minimumDefault, const Decimal& maximumDefault, const StepRange::StepDescription&) const;
 
 private:
     // Helper for stepUp()/stepDown(). Adds step value * count to the current value.
     void applyStep(const Decimal&, int count, AnyStepHandling, TextFieldEventBehavior, ExceptionState&);
 };
 
 } // namespace WebCore
 #endif