Oilpan: cleanup based on review comments after removal of TreeShared.

Source/core/dom/StyleEngine.h

 /*
  * 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, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
@@ skipping 185 matching lines @@
     StyleEngine(Document&);
 
     TreeScopeStyleSheetCollection* ensureStyleSheetCollectionFor(TreeScope&);
     TreeScopeStyleSheetCollection* styleSheetCollectionFor(TreeScope&);
     bool shouldUpdateShadowTreeStyleSheetCollection(StyleResolverUpdateMode);
 
     void markTreeScopeDirty(TreeScope&);
 
     bool isMaster() const { return m_isMaster; }
     Document* master();
+    Document& document() const { return *m_document; }
 
     typedef ListHashSet<TreeScope*, 16> TreeScopeSet;
     static void insertTreeScopeInDocumentOrder(TreeScopeSet&, TreeScope*);
     void clearMediaQueryRuleSetOnTreeScopeStyleSheets(TreeScopeSet treeScopes);
 
     void createResolver();
 
     static PassRefPtrWillBeRawPtr<CSSStyleSheet> parseSheet(Element*, const String& text, TextPosition startPosition, bool createdByParser);
 
     RawPtrWillBeMember<Document> m_document;
@@ skipping 34 matching lines @@
 
     RefPtrWillBeMember<CSSFontSelector> m_fontSelector;
 
     WillBeHeapHashMap<AtomicString, RawPtrWillBeMember<StyleSheetContents> > m_textToSheetCache;
     WillBeHeapHashMap<RawPtrWillBeMember<StyleSheetContents>, AtomicString> m_sheetToTextCache;
 };
 
 }
 
 #endif