Allow "::content /deep/" to match.

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/)
  * Copyright (c) 2011, Code Aurora Forum. All rights reserved.
  * Copyright (C) Research In Motion Limited 2011. All rights reserved.
@@ skipping 332 matching lines @@
             if (!shadowHost)
                 return SelectorFailsCompletely;
             nextContext.element = shadowHost;
             nextContext.isSubSelector = false;
             nextContext.elementStyle = 0;
             return this->match(nextContext, siblingTraversalStrategy, result);
         }
 
     case CSSSelector::ShadowDeep:
         {
+            if (context.selector->relationIsAffectedByPseudoContent()) {
+                for (Element* element = context.element; element; element = parentOrShadowHostButDisallowEscapingClosedShadowTree(*element)) {
+                    if (matchForShadowDistributed(element, siblingTraversalStrategy, nextContext, result) == SelectorMatches)
+                        return SelectorMatches;
+                }
+                return SelectorFailsCompletely;
+            }
+
             nextContext.isSubSelector = false;
             nextContext.elementStyle = 0;
             for (nextContext.element = parentOrShadowHostButDisallowEscapingClosedShadowTree(*context.element); nextContext.element; nextContext.element = parentOrShadowHostButDisallowEscapingClosedShadowTree(*nextContext.element)) {
                 Match match = this->match(nextContext, siblingTraversalStrategy, result);
                 if (match == SelectorMatches || match == SelectorFailsCompletely)
                     return match;
                 if (nextSelectorExceedsScope(nextContext))
                     return SelectorFailsCompletely;
             }
             return SelectorFailsCompletely;
@@ skipping 830 matching lines @@
     return isHTMLSelectElement(element) && !toHTMLSelectElement(element).usesMenuList();
 }
 
 template
 SelectorChecker::Match SelectorChecker::match(const SelectorCheckingContext&, const DOMSiblingTraversalStrategy&, MatchResult*) const;
 
 template
 SelectorChecker::Match SelectorChecker::match(const SelectorCheckingContext&, const ShadowDOMSiblingTraversalStrategy&, MatchResult*) const;
 
 }