Add a UseCounter for '>>>' combinator.

third_party/WebKit/Source/core/css/SelectorChecker.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc.
  * All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved.
  * (http://www.torchmobile.com/)
@@ skipping 430 matching lines @@
         if (match == SelectorMatches || match == SelectorFailsCompletely)
           return match;
         if (nextSelectorExceedsScope(nextContext))
           return SelectorFailsCompletely;
       }
       return SelectorFailsCompletely;
     }
 
     case CSSSelector::ShadowPiercingDescendant: {
       DCHECK(m_isQuerySelector);
+      UseCounter::count(context.element->document(),
+                        UseCounter::CSSShadowPiercingDescendantCombinator);
       // TODO(kochi): parentOrOpenShadowHostElement() is necessary because
       // SelectorQuery can pass V0 shadow roots. All closed shadow roots are
       // already filtered out, thus once V0 is removed this logic can use
       // parentOrShadowHostElement() instead.
       for (nextContext.element =
                parentOrOpenShadowHostElement(*context.element);
            nextContext.element;
            nextContext.element =
                parentOrOpenShadowHostElement(*nextContext.element)) {
         Match match = matchSelector(nextContext, result);
@@ skipping 844 matching lines @@
 }
 
 bool SelectorChecker::matchesFocusPseudoClass(const Element& element) {
   if (InspectorInstrumentation::forcePseudoState(const_cast<Element*>(&element),
                                                  CSSSelector::PseudoFocus))
     return true;
   return element.isFocused() && isFrameFocused(element);
 }
 
 }  // namespace blink