Fix problems on changing 'multiple' state SELECT element to 'single' state.

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

 /*
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
  * 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, 2009, 2010, 2011 Apple Inc. All rights reserved.
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2010 Google Inc. All rights reserved.
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
@@ skipping 426 matching lines @@
             cache->childrenChanged(this);
     }
 }
 
 void HTMLSelectElement::accessKeyAction(bool sendMouseEvents)
 {
     focus();
     dispatchSimulatedClick(nullptr, sendMouseEvents ? SendMouseUpDownEvents : SendNoEvents);
 }
 
-void HTMLSelectElement::setMultiple(bool multiple)
-{
-    bool oldMultiple = this->multiple();
-    int oldSelectedIndex = selectedIndex();
-    setAttribute(multipleAttr, multiple ? emptyAtom : nullAtom);
-
-    // Restore selectedIndex after changing the multiple flag to preserve
-    // selection as single-line and multi-line has different defaults.
-    if (oldMultiple != this->multiple())
-        selectOption(oldSelectedIndex, DeselectOtherOptions);
-}
-
 void HTMLSelectElement::setSize(unsigned size)
 {
     setUnsignedIntegralAttribute(sizeAttr, size);
 }
 
 Element* HTMLSelectElement::namedItem(const AtomicString& name)
 {
     return options()->namedItem(name);
 }
 
@@ skipping 758 matching lines @@
             }
         }
     }
 
     setOptionsChangedOnLayoutObject();
     setNeedsValidityCheck();
 }
 
 void HTMLSelectElement::parseMultipleAttribute(const AtomicString& value)
 {
+    bool oldMultiple = m_multiple;
+    int oldSelectedIndex = selectedIndex();
     m_multiple = !value.isNull();
     setNeedsValidityCheck();
-
     lazyReattachIfAttached();
+    // Restore selectedIndex after changing the multiple flag to preserve
+    // selection as single-line and multi-line has different defaults.
+    if (oldMultiple != m_multiple) {
+        // Preserving the first selection is compatible with Firefox and
+        // WebKit. However Edge seems to "ask for a reset" simply.  As of 2016
+        // March, the HTML specification says nothing about this.
+        if (oldSelectedIndex >= 0)
+            selectOption(oldSelectedIndex, DeselectOtherOptions);
+        else
+            resetToDefaultSelection();
+    }
 }
 
 void HTMLSelectElement::appendToFormData(FormData& formData)
 {
     const AtomicString& name = this->name();
     if (name.isEmpty())
         return;
 
     for (auto& element : listItems()) {
         if (isHTMLOptionElement(*element) && toHTMLOptionElement(*element).selected() && !toHTMLOptionElement(*element).isDisabledFormControl())
@@ skipping 736 matching lines @@
     m_popupIsVisible = false;
     m_popup = nullptr;
 }
 
 void HTMLSelectElement::resetTypeAheadSessionForTesting()
 {
     m_typeAhead.resetSession();
 }
 
 } // namespace blink