Avoid always style recalc when removing stylesheets.

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 36 matching lines @@
     bool isNewEntry;
     ScopedStyleResolver* scopedStyleResolver = addScopedStyleResolver(scopingNode, isNewEntry);
     if (isNewEntry)
         setupScopedStylesTree(scopedStyleResolver);
     return scopedStyleResolver;
 }
 
 ScopedStyleResolver* ScopedStyleTree::scopedStyleResolverFor(const ContainerNode& scopingNode)
 {
     if (!scopingNode.hasScopedHTMLStyleChild()
-        && !(scopingNode.isElementNode() && toElement(scopingNode).shadow())
+        && !isShadowHost(&scopingNode)
         && !scopingNode.isDocumentNode()
         && !scopingNode.isShadowRoot())
         return 0;
-    HashMap<const ContainerNode*, OwnPtr<ScopedStyleResolver> >::iterator it = m_authorStyles.find(&scopingNode);
-    return it != m_authorStyles.end() ? it->value.get() : 0;
+    return lookupScopedStyleResolverFor(&scopingNode);
 }
 
 ScopedStyleResolver* ScopedStyleTree::addScopedStyleResolver(const ContainerNode& scopingNode, bool& isNewEntry)
 {
     HashMap<const ContainerNode*, OwnPtr<ScopedStyleResolver> >::AddResult addResult = m_authorStyles.add(&scopingNode, nullptr);
 
     if (addResult.isNewEntry) {
         addResult.iterator->value = ScopedStyleResolver::create(scopingNode);
         if (scopingNode.isDocumentNode())
             m_scopedResolverForDocument = addResult.iterator->value.get();
@@ skipping 354 matching lines @@
 
 void ScopedStyleResolver::collectViewportRulesTo(StyleResolver* resolver) const
 {
     // Only consider the global author RuleSet for @viewport rules.
     ASSERT(m_scopingNode.isDocumentNode());
     if (m_authorStyle)
         resolver->viewportStyleResolver()->collectViewportRules(m_authorStyle.get(), ViewportStyleResolver::AuthorOrigin);
 }
 
 } // namespace WebCore