HTMLOptionElement.prototype.selected setter should not make an option dirty if it doesn't change it…

third_party/WebKit/Source/core/html/HTMLOptionElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2004, 2005, 2006, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google Inc. All rights reserved.
  * Copyright (C) 2011 Motorola Mobility, Inc.  All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 249 matching lines @@
         select->optionSelectionStateChanged(this, selected);
 }
 
 bool HTMLOptionElement::selectedForBinding() const
 {
     return selected();
 }
 
 void HTMLOptionElement::setSelectedForBinding(bool selected)
 {
+    bool wasSelected = m_isSelected;
     setSelected(selected);
+
+    // As of December 2015, the HTML specification says the dirtiness becomes

[tfarina, 2015/12/23 23:04:36]

is it worth pointing to the link for that specification?

+    // true by |selected| setter unconditionally. However it caused a real bug,
+    // crbug.com/570367, and is not compatible with other browsers.
+    // Firefox seems not to set dirtiness if an option is owned by a select
+    // element and selectedness is not changed.
+    if (ownerSelectElement() && wasSelected == m_isSelected)
+        return;
+
     m_isDirty = true;
 }
 
 void HTMLOptionElement::setSelectedState(bool selected)
 {
     if (m_isSelected == selected)
         return;
 
     m_isSelected = selected;
     pseudoStateChanged(CSSSelector::PseudoChecked);
@@ skipping 178 matching lines @@
         ASSERT(parent);
         if (isHTMLOptGroupElement(*parent)) {
             const ComputedStyle* parentStyle = parent->computedStyle() ? parent->computedStyle() : parent->ensureComputedStyle();
             return !parentStyle || parentStyle->display() == NONE;
         }
     }
     return m_style->display() == NONE;
 }
 
 } // namespace blink