Reset SelectorCheckingContext.elementStyle for :ancestor matching.

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 886 matching lines @@
 
                 bool matched = false;
                 unsigned maxSpecificity = 0;
 
                 // If one of simple selectors matches an element, returns SelectorMatches. Just "OR".
                 for (subContext.selector = selector.selectorList()->first(); subContext.selector; subContext.selector = CSSSelectorList::next(*subContext.selector)) {
                     subContext.behaviorAtBoundary = ScopeIsShadowHostInPseudoHostParameter;
                     subContext.scope = shadowHost;
                     // Use NodeRenderingTraversal to traverse a composed ancestor list of a given element.
                     Element* nextElement = &element;
+                    SelectorCheckingContext hostContext(subContext);
                     do {
                         MatchResult subResult;
-                        subContext.element = nextElement;
-                        if (match(subContext, siblingTraversalStrategy, &subResult) == SelectorMatches) {
+                        hostContext.element = nextElement;
+                        if (match(hostContext, siblingTraversalStrategy, &subResult) == SelectorMatches) {
                             matched = true;
                             // Consider div:host(div:host(div:host(div:host...))).
-                            maxSpecificity = std::max(maxSpecificity, subContext.selector->specificity() + subResult.specificity);
+                            maxSpecificity = std::max(maxSpecificity, hostContext.selector->specificity() + subResult.specificity);
                             break;
                         }
-                        subContext.behaviorAtBoundary = DoesNotCrossBoundary;
-                        subContext.scope = 0;
+                        hostContext.behaviorAtBoundary = DoesNotCrossBoundary;
+                        hostContext.scope = 0;
 
                         if (selector.pseudoType() == CSSSelector::PseudoHost)
                             break;
 
+                        hostContext.elementStyle = 0;
                         nextElement = NodeRenderingTraversal::parentElement(nextElement);
                     } while (nextElement);
                 }
                 if (matched) {
                     if (specificity)
                         *specificity = maxSpecificity;
                     return true;
                 }
             }
             break;
@@ skipping 169 matching lines @@
     return element.focused() && isFrameFocused(element);
 }
 
 template
 SelectorChecker::Match SelectorChecker::match(const SelectorCheckingContext&, const DOMSiblingTraversalStrategy&, MatchResult*) const;
 
 template
 SelectorChecker::Match SelectorChecker::match(const SelectorCheckingContext&, const ShadowDOMSiblingTraversalStrategy&, MatchResult*) const;
 
 }