Avoid style sharing with mis-matched descendant selectors

Source/core/css/RuleSet.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 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 206 matching lines @@
     , m_propertyWhitelistType(determinePropertyWhitelistType(addRuleFlags, selector()))
 {
     ASSERT(m_position == position);
     ASSERT(m_selectorIndex == selectorIndex);
     SelectorFilter::collectIdentifierHashes(selector(), m_descendantSelectorIdentifierHashes, maximumIdentifierCount);
 }
 
 static void collectFeaturesFromRuleData(RuleFeatureSet& features, const RuleData& ruleData)
 {
     bool foundSiblingSelector = false;
+    bool foundDescendantSelector = false;
     for (const CSSSelector* selector = ruleData.selector(); selector; selector = selector->tagHistory()) {
         features.collectFeaturesFromSelector(selector);
 
         if (const CSSSelectorList* selectorList = selector->selectorList()) {
             for (const CSSSelector* subSelector = selectorList->first(); subSelector; subSelector = CSSSelectorList::next(subSelector)) {
                 if (!foundSiblingSelector && selector->isSiblingSelector())
                     foundSiblingSelector = true;
                 features.collectFeaturesFromSelector(subSelector);
             }
-        } else if (!foundSiblingSelector && selector->isSiblingSelector())
+        } else if (!foundSiblingSelector && selector->isSiblingSelector()) {
             foundSiblingSelector = true;
+        } else if (!foundDescendantSelector && selector->relation() == CSSSelector::Descendant) {
+            foundDescendantSelector = true;
+        }
     }
     if (foundSiblingSelector)
         features.siblingRules.append(RuleFeature(ruleData.rule(), ruleData.selectorIndex(), ruleData.hasDocumentSecurityOrigin()));
+    if (foundDescendantSelector)
+        features.descendantRules.append(RuleFeature(ruleData.rule(), ruleData.selectorIndex(), ruleData.hasDocumentSecurityOrigin()));
     if (ruleData.containsUncommonAttributeSelector())
         features.uncommonAttributeRules.append(RuleFeature(ruleData.rule(), ruleData.selectorIndex(), ruleData.hasDocumentSecurityOrigin()));
 }
 
 void RuleSet::addToRuleSet(StringImpl* key, PendingRuleMap& map, const RuleData& ruleData)
 {
     if (!key)
         return;
     OwnPtr<LinkedStack<RuleData> >& rules = map.add(key, nullptr).iterator->value;
     if (!rules)
@@ skipping 204 matching lines @@
     compactPendingRules(pendingRules->shadowPseudoElementRules, m_shadowPseudoElementRules);
     m_linkPseudoClassRules.shrinkToFit();
     m_cuePseudoRules.shrinkToFit();
     m_focusPseudoClassRules.shrinkToFit();
     m_universalRules.shrinkToFit();
     m_pageRules.shrinkToFit();
     m_viewportRules.shrinkToFit();
 }
 
 } // namespace WebCore