Oilpan: Trace MediaQueryMacher::m_document.

Source/core/css/MediaQueryMatcher.cpp

 /*
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  *
  *  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,
  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 43 matching lines @@
     , m_evaluationRound(1)
 {
     ASSERT(m_document);
 }
 
 DEFINE_EMPTY_DESTRUCTOR_WILL_BE_REMOVED(MediaQueryMatcher)
 
 void MediaQueryMatcher::documentDestroyed()
 {
     m_listeners.clear();
-    m_document = 0;
+    m_document = nullptr;
 }
 
 AtomicString MediaQueryMatcher::mediaType() const
 {
     if (!m_document || !m_document->frame() || !m_document->frame()->view())
         return nullAtom;
 
     return m_document->frame()->view()->mediaType();
 }
 
@@ skipping 60 matching lines @@
     OwnPtr<MediaQueryEvaluator> evaluator = prepareEvaluator();
     if (!evaluator)
         return;
 
     for (size_t i = 0; i < m_listeners.size(); ++i)
         m_listeners[i]->evaluate(evaluator.get());
 }
 
 void MediaQueryMatcher::trace(Visitor* visitor)
 {
+    visitor->trace(m_document);
     // We don't support tracing of vectors of OwnPtrs (ie. Vector<OwnPtr<Listener> >).
     // Since this is a transitional object we are just ifdef'ing it out when oilpan is not enabled.
 #if ENABLE(OILPAN)
     visitor->trace(m_listeners);
 #endif
 }
 
 }