Use weak members to cache StyleSheetContents.

third_party/WebKit/Source/core/css/CSSStyleSheet.cpp

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2006, 2007, 2012 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 129 matching lines @@
 static bool isStyleElement(const Node* node)
 {
     return node && (isHTMLStyleElement(node) || isSVGStyleElement(node));
 }
 
 #endif // ENABLE(ASSERT)
 
 void CSSStyleSheet::willMutateRules()
 {
     // If we are the only client it is safe to mutate.
-    if (m_contents->clientSize() <= 1 && !m_contents->isReferencedFromResource()) {
+    if (!m_contents->isUsedFromTextCache() && !m_contents->isReferencedFromResource()) {
         m_contents->clearRuleSet();
-        if (Document* document = ownerDocument())
-            m_contents->removeSheetFromCache(document);
         m_contents->setMutable();
         return;
     }
     // Only cacheable stylesheets should have multiple clients.
     ASSERT((isStyleElement(ownerNode()) && m_contents->isCacheableForStyleElement())
         || m_contents->isCacheableForResource());
 
     // Copy-on-write.
     m_contents->unregisterClient(this);
     m_contents = m_contents->copy();
@@ skipping 276 matching lines @@
     visitor->trace(m_mediaQueries);
     visitor->trace(m_ownerNode);
     visitor->trace(m_ownerRule);
     visitor->trace(m_mediaCSSOMWrapper);
     visitor->trace(m_childRuleCSSOMWrappers);
     visitor->trace(m_ruleListCSSOMWrapper);
     StyleSheet::trace(visitor);
 }
 
 } // namespace blink