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

Source/core/css/resolver/ScopedStyleResolver.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 110 matching lines @@
     RuleRange ruleRange = collector.matchedResult().ranges.authorRuleRange();
     ASSERT(!collector.scopeContainsLastMatchedElement());
     collector.setScopeContainsLastMatchedElement(true);
     for (size_t i = 0; i < m_authorStyleSheets.size(); ++i) {
         MatchRequest matchRequest(&m_authorStyleSheets[i]->contents()->ruleSet(), includeEmptyRules, &m_scope->rootNode(), m_authorStyleSheets[i], i);
         collector.collectMatchingRules(matchRequest, ruleRange, cascadeScope, cascadeOrder);
     }
     collector.setScopeContainsLastMatchedElement(false);
 }
 
+void ScopedStyleResolver::collectMatchingShadowHostRules(ElementRuleCollector& collector, bool includeEmptyRules, CascadeScope cascadeScope, CascadeOrder cascadeOrder)
+{
+    RuleRange ruleRange = collector.matchedResult().ranges.authorRuleRange();
+    ASSERT(!collector.scopeContainsLastMatchedElement());
+    collector.setScopeContainsLastMatchedElement(true);
+    for (size_t i = 0; i < m_authorStyleSheets.size(); ++i) {
+        MatchRequest matchRequest(&m_authorStyleSheets[i]->contents()->ruleSet(), includeEmptyRules, &m_scope->rootNode(), m_authorStyleSheets[i], i);
+        collector.collectMatchingShadowHostRules(matchRequest, ruleRange, cascadeScope, cascadeOrder);
+    }
+    collector.setScopeContainsLastMatchedElement(false);
+}
+
 void ScopedStyleResolver::matchPageRules(PageRuleCollector& collector)
 {
     // Only consider the global author RuleSet for @page rules, as per the HTML5 spec.
     ASSERT(m_scope->rootNode().isDocumentNode());
     for (size_t i = 0; i < m_authorStyleSheets.size(); ++i)
         collector.matchPageRules(&m_authorStyleSheets[i]->contents()->ruleSet());
 }
 
 void ScopedStyleResolver::collectViewportRulesTo(StyleResolver* resolver) const
 {
     if (!m_scope->rootNode().isDocumentNode())
         return;
     for (size_t i = 0; i < m_authorStyleSheets.size(); ++i)
         resolver->viewportStyleResolver()->collectViewportRules(&m_authorStyleSheets[i]->contents()->ruleSet(), ViewportStyleResolver::AuthorOrigin);
 }
 
 void ScopedStyleResolver::trace(Visitor* visitor)
 {
 #if ENABLE(OILPAN)
     visitor->trace(m_scope);
     visitor->trace(m_authorStyleSheets);
     visitor->trace(m_keyframesRuleMap);
 #endif
 }
 
 } // namespace blink