Make RenderObject::style() return a const object

Source/core/dom/Document.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 771 matching lines @@
 
     HTMLElement* body() const;
     void setBody(PassRefPtrWillBeRawPtr<HTMLElement>, ExceptionState&);
 
     HTMLHeadElement* head() const;
 
     // Decide which element is to define the viewport's overflow policy. If |rootStyle| is set, use
     // that as the style for the root element, rather than obtaining it on our own. The reason for
     // this is that style may not have been associated with the elements yet - in which case it may
     // have been calculated on the fly (without associating it with the actual element) somewhere.
-    Element* viewportDefiningElement(LayoutStyle* rootStyle = nullptr) const;
+    Element* viewportDefiningElement(const LayoutStyle* rootStyle = nullptr) const;
 
     DocumentMarkerController& markers() const { return *m_markers; }
 
     bool execCommand(const String& command, bool showUI, const String& value);
     bool queryCommandEnabled(const String& command);
     bool queryCommandIndeterm(const String& command);
     bool queryCommandState(const String& command);
     bool queryCommandSupported(const String& command);
     String queryCommandValue(const String& command);
 
@@ skipping 623 matching lines @@
 DEFINE_TYPE_CASTS(TreeScope, Document, document, true, true);
 
 } // namespace blink
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showLiveDocumentInstances();
 #endif
 
 #endif // Document_h