Use counter for tabStop.

Source/core/dom/Element.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Peter Kelly (pmk@post.com)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012, 2013 Apple Inc. All rights reserved.
  *           (C) 2007 Eric Seidel (eric@webkit.org)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 2082 matching lines @@
             if (treeScope().adjustedFocusedElement() == this) {
                 // We might want to call blur(), but it's dangerous to dispatch
                 // events here.
                 document().setNeedsFocusedElementCheck();
             }
         } else if (parseHTMLInteger(value, tabindex)) {
             // Clamp tabindex to the range of 'short' to match Firefox's behavior.
             setTabIndexExplicitly(max(static_cast<int>(std::numeric_limits<short>::min()), std::min(tabindex, static_cast<int>(std::numeric_limits<short>::max()))));
         }
     } else if (RuntimeEnabledFeatures::tabStopAttributeEnabled() && name == tabstopAttr) {
+        UseCounter::count(document(), UseCounter::TabStopAttribute);
         if (!hasAttribute(tabstopAttr)) {
             // tabstop attribute removed.
             clearElementFlag(TabStopWasSetExplicitly);
             setTabStopInternal(tabIndex() >= 0);
         } else {
             // Treat empty attribute as true.
             if (equalIgnoringCase(value, "true") || equalIgnoringCase(value, "")) {
                 setTabStopInternal(true);
                 setElementFlag(TabStopWasSetExplicitly, true);
             } else if (equalIgnoringCase(value, "false")) {
@@ skipping 1382 matching lines @@
 {
 #if ENABLE(OILPAN)
     if (hasRareData())
         visitor->trace(elementRareData());
     visitor->trace(m_elementData);
 #endif
     ContainerNode::trace(visitor);
 }
 
 } // namespace blink