Keep a separate list of :host(-context) rules.

Source/core/css/ElementRuleCollector.cpp

Index: Source/core/css/ElementRuleCollector.cpp
diff --git a/Source/core/css/ElementRuleCollector.cpp b/Source/core/css/ElementRuleCollector.cpp
index d7c7a0e596bc0ab06ef9ca89b5d1db75176712e3..dc50c06831ff9b4c92593165f62073531fa34352 100644
--- a/Source/core/css/ElementRuleCollector.cpp
+++ b/Source/core/css/ElementRuleCollector.cpp
@@ -174,6 +174,11 @@ void ElementRuleCollector::collectMatchingRules(const MatchRequest& matchRequest
     collectMatchingRulesForList(matchRequest.ruleSet->universalRules(), cascadeScope, cascadeOrder, matchRequest, ruleRange);
 }
 
+void ElementRuleCollector::collectMatchingShadowHostRules(const MatchRequest& matchRequest, RuleRange& ruleRange, CascadeScope cascadeScope, CascadeOrder cascadeOrder, bool matchingTreeBoundaryRules)
+{
+    collectMatchingRulesForList(matchRequest.ruleSet->shadowHostRules(), cascadeScope, cascadeOrder, matchRequest, ruleRange);
+}
+
 CSSRuleList* ElementRuleCollector::nestedRuleList(CSSRule* rule)
 {
     switch (rule->type()) {