Oilpan: Use weak pointers in StyleSheetContents caches.

Source/core/css/StyleSheetContents.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 79 matching lines @@
 
     // FIXME: Copy import rules.
     ASSERT(o.m_importRules.isEmpty());
 
     for (unsigned i = 0; i < m_childRules.size(); ++i)
         m_childRules[i] = o.m_childRules[i]->copy();
 }
 
 StyleSheetContents::~StyleSheetContents()
 {
+#if !ENABLE(OILPAN)
     StyleEngine::removeSheet(this);
-#if !ENABLE(OILPAN)
     clearRules();
 #endif
 }
 
 void StyleSheetContents::setHasSyntacticallyValidCSSHeader(bool isValidCss)
 {
     if (maybeCacheable() && !isValidCss)
         StyleEngine::removeSheet(this);
     m_hasSyntacticallyValidCSSHeader = isValidCss;
 }
@@ skipping 504 matching lines @@
 }
 
 void StyleSheetContents::trace(Visitor* visitor)
 {
     visitor->trace(m_ownerRule);
     visitor->trace(m_importRules);
     visitor->trace(m_childRules);
 }
 
 }