Avoid style sharing with mis-matched descendant selectors

Source/core/css/RuleSet.cpp

Index: Source/core/css/RuleSet.cpp
diff --git a/Source/core/css/RuleSet.cpp b/Source/core/css/RuleSet.cpp
index 3509682031c0404611d0c8beebed29a99da5f896..120c45185a4a1569fecff7d77e96a2478b06608f 100644
--- a/Source/core/css/RuleSet.cpp
+++ b/Source/core/css/RuleSet.cpp
@@ -224,6 +224,7 @@ RuleData::RuleData(StyleRule* rule, unsigned selectorIndex, unsigned position, A
 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);
 
@@ -233,11 +234,16 @@ static void collectFeaturesFromRuleData(RuleFeatureSet& features, const RuleData
                     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()));
 }