StyleResolver should update RuleSets lazily.

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 229 matching lines @@
     if (!styleElement->scoped())
         return styleElement->isInShadowTree() ? styleElement->containingShadowRoot() : 0;
 
     ContainerNode* parent = styleElement->parentNode();
     if (!parent)
         return 0;
 
     return (parent->isElementNode() || parent->isShadowRoot()) ? parent : 0;
 }
 
-void ScopedStyleResolver::addRulesFromSheet(StyleSheetContents* sheet, const MediaQueryEvaluator& medium, StyleResolver* resolver)
+inline RuleSet* ScopedStyleResolver::ensureAuthorStyle()
 {
     if (!m_authorStyle)
         m_authorStyle = RuleSet::create();
-    m_authorStyle->addRulesFromSheet(sheet, medium, resolver, &m_scopingNode);
+    return m_authorStyle.get();
+}
+
+void ScopedStyleResolver::addRulesFromSheet(StyleSheetContents* sheet, const MediaQueryEvaluator& medium, StyleResolver* resolver, bool viewportRuleIsProcessed)
+{
+    ensureAuthorStyle()->addRulesFromSheet(sheet, medium, resolver, &m_scopingNode, viewportRuleIsProcessed);
     resolver->processScopedRules(*m_authorStyle, sheet->baseURL(), &m_scopingNode);
 }
 
+void ScopedStyleResolver::addViewportRule(StyleRuleViewport* rule)
+{
+    ensureAuthorStyle()->addViewportRule(rule);
+}
+
 inline RuleSet* ScopedStyleResolver::ensureAtHostRuleSetFor(const ShadowRoot* shadowRoot)
 {
     HashMap<const ShadowRoot*, OwnPtr<RuleSet> >::AddResult addResult = m_atHostRules.add(shadowRoot, nullptr);
     if (addResult.isNewEntry)
         addResult.iterator->value = RuleSet::create();
     return addResult.iterator->value.get();
 }
 
 void ScopedStyleResolver::addHostRule(StyleRuleHost* hostRule, bool hasDocumentSecurityOrigin, const ContainerNode* scopingNode)
 {
@@ skipping 160 matching lines @@
 
 void ScopedStyleResolver::collectViewportRulesTo(StyleResolver* resolver) const
 {
     // Only consider the global author RuleSet for @viewport rules.
     if (!m_scopingNode.isDocumentNode() || !m_authorStyle)
         return;
     resolver->viewportStyleResolver()->collectViewportRules(m_authorStyle.get(), ViewportStyleResolver::AuthorOrigin);
 }
 
 } // namespace WebCore