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

Source/core/html/forms/InputType.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, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2007 Samuel Weinig (sam@webkit.org)
  * Copyright (C) 2009, 2010, 2011, 2012 Google Inc. All rights reserved.
  * Copyright (C) 2012 Samsung Electronics. All rights reserved.
  *
@@ skipping 529 matching lines @@
 bool InputType::shouldSendChangeEventAfterCheckedChanged()
 {
     return true;
 }
 
 bool InputType::storesValueSeparateFromAttribute()
 {
     return true;
 }
 
+bool InputType::shouldDispatchFormControlChangeEvent(String& oldValue, String& newValue)
+{
+    return !equalIgnoringNullity(oldValue, newValue);
+}
+
 void InputType::setValue(const String& sanitizedValue, bool valueChanged, TextFieldEventBehavior eventBehavior)
 {
     element().setValueInternal(sanitizedValue, eventBehavior);
     element().setNeedsStyleRecalc(SubtreeStyleChange);
     if (!valueChanged)
         return;
     switch (eventBehavior) {
     case DispatchChangeEvent:
         element().dispatchFormControlChangeEvent();
         break;
@@ skipping 399 matching lines @@
 StepRange InputType::createStepRange(AnyStepHandling anyStepHandling, const Decimal& stepBaseDefault, const Decimal& minimumDefault, const Decimal& maximumDefault, const StepRange::StepDescription& stepDescription) const
 {
     const Decimal stepBase = findStepBase(stepBaseDefault);
     const Decimal minimum = parseToNumber(element().fastGetAttribute(minAttr), minimumDefault);
     const Decimal maximum = parseToNumber(element().fastGetAttribute(maxAttr), maximumDefault);
     const Decimal step = StepRange::parseStep(anyStepHandling, stepDescription, element().fastGetAttribute(stepAttr));
     return StepRange(stepBase, minimum, maximum, step, stepDescription);
 }
 
 } // namespace WebCore