Move StyleSheet to the oilpan heap using transition types.

Source/core/css/MediaList.cpp

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2006, 2010, 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 158 matching lines @@
 
 MediaList::MediaList(MediaQuerySet* mediaQueries, CSSStyleSheet* parentSheet)
     : m_mediaQueries(mediaQueries)
     , m_parentStyleSheet(parentSheet)
     , m_parentRule(nullptr)
 {
 }
 
 MediaList::MediaList(MediaQuerySet* mediaQueries, CSSRule* parentRule)
     : m_mediaQueries(mediaQueries)
-    , m_parentStyleSheet(0)
+    , m_parentStyleSheet(nullptr)
     , m_parentRule(parentRule)
 {
 }
 
 MediaList::~MediaList()
 {
 }
 
 void MediaList::setMediaText(const String& value)
 {
@@ skipping 42 matching lines @@
 
 void MediaList::reattach(MediaQuerySet* mediaQueries)
 {
     ASSERT(mediaQueries);
     m_mediaQueries = mediaQueries;
 }
 
 void MediaList::trace(Visitor* visitor)
 {
     visitor->trace(m_mediaQueries);
+    visitor->trace(m_parentStyleSheet);
     visitor->trace(m_parentRule);
 }
 
 static void addResolutionWarningMessageToConsole(Document* document, const String& serializedExpression, const CSSPrimitiveValue* value)
 {
     ASSERT(document);
     ASSERT(value);
 
     DEFINE_STATIC_LOCAL(String, mediaQueryMessage, ("Consider using 'dppx' units instead of '%replacementUnits%', as in CSS '%replacementUnits%' means dots-per-CSS-%lengthUnit%, not dots-per-physical-%lengthUnit%, so does not correspond to the actual '%replacementUnits%' of a screen. In media query expression: "));
     DEFINE_STATIC_LOCAL(String, mediaValueDPI, ("dpi"));
@@ skipping 46 matching lines @@
                     CSSPrimitiveValue* primitiveValue = toCSSPrimitiveValue(cssValue);
                     if (primitiveValue->isDotsPerInch() || primitiveValue->isDotsPerCentimeter())
                         addResolutionWarningMessageToConsole(document, mediaQuerySet->mediaText(), primitiveValue);
                 }
             }
         }
     }
 }
 
 }