HTMLImportsController does not need to hold Document ptr.

Source/core/dom/StyleEngine.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) Research In Motion Limited 2010-2011. All rights reserved.
@@ skipping 37 matching lines @@
 #include "core/frame/Settings.h"
 #include "core/svg/SVGStyleElement.h"
 #include "platform/URLPatternMatcher.h"
 
 namespace WebCore {
 
 using namespace HTMLNames;
 
 StyleEngine::StyleEngine(Document& document)
     : m_document(&document)
-    , m_isMaster(!document.importsController() || document.importsController()->isMaster(document) )
+    , m_isMaster(!document.importsController() || document.importsController()->master() == &document)
     , m_pendingStylesheets(0)
     , m_injectedStyleSheetCacheValid(false)
 #if ENABLE(OILPAN)
     , m_documentStyleSheetCollection(new DocumentStyleSheetCollection(document))
 #else
     , m_documentStyleSheetCollection(document)
 #endif
     , m_documentScopeDirty(true)
     , m_usesSiblingRules(false)
     , m_usesSiblingRulesOverride(false)
@@ skipping 572 matching lines @@
     visitor->trace(m_authorStyleSheets);
     visitor->trace(m_documentStyleSheetCollection);
     visitor->trace(m_styleSheetCollectionMap);
     visitor->trace(m_resolver);
     visitor->trace(m_fontSelector);
     visitor->trace(m_textToSheetCache);
     visitor->trace(m_sheetToTextCache);
 }
 
 }