Regression: Add back support for hr elements in select listbox

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 1745 matching lines @@
 {
 #if ENABLE(OILPAN)
     visitor->trace(m_listItems);
 #endif
     HTMLFormControlElementWithState::trace(visitor);
 }
 
 void HTMLSelectElement::didAddUserAgentShadowRoot(ShadowRoot& root)
 {
     RefPtrWillBeRawPtr<HTMLContentElement> content = HTMLContentElement::create(document());
-    content->setAttribute(selectAttr, "option,optgroup");
+    content->setAttribute(selectAttr, "option,optgroup,hr");
     root.appendChild(content);
 }
 
 HTMLOptionElement* HTMLSelectElement::spatialNavigationFocusedOption()
 {
     if (!isSpatialNavigationEnabled(document().frame()))
         return nullptr;
     int focusedIndex = activeSelectionEndListIndex();
     if (focusedIndex < 0)
         focusedIndex = firstSelectableListIndex();
     if (focusedIndex < 0)
         return nullptr;
     HTMLElement* focused = listItems()[focusedIndex];
     return isHTMLOptionElement(focused) ? toHTMLOptionElement(focused) : nullptr;
 }
 
 } // namespace