Make RenderObject::style() return a const object

Source/core/css/resolver/StyleAdjuster.h

 /*
  * Copyright (C) 2013 Google, Inc.
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 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.
  *
@@ skipping 23 matching lines @@
 // Certain CSS Properties/Values do not apply to certain elements
 // and the web expects that we expose "adjusted" values when
 // for those property/element pairs.
 class StyleAdjuster {
     STACK_ALLOCATED();
 public:
     StyleAdjuster(bool useQuirksModeStyles)
         : m_useQuirksModeStyles(useQuirksModeStyles)
     { }
 
-    void adjustRenderStyle(RenderStyle* styleToAdjust, RenderStyle* parentStyle, Element*, const CachedUAStyle*);
+    void adjustRenderStyle(RenderStyle* styleToAdjust, const RenderStyle* parentStyle, Element*, const CachedUAStyle*);
 
 private:
     void adjustStyleForFirstLetter(RenderStyle*);
-    void adjustStyleForDisplay(RenderStyle* styleToAdjust, RenderStyle* parentStyle);
-    void adjustStyleForHTMLElement(RenderStyle* styleToAdjust, RenderStyle* parentStyle, HTMLElement&);
+    void adjustStyleForDisplay(RenderStyle* styleToAdjust, const RenderStyle* parentStyle);
+    void adjustStyleForHTMLElement(RenderStyle* styleToAdjust, const RenderStyle* parentStyle, HTMLElement&);
     void adjustOverflow(RenderStyle* styleToAdjust);
     void adjustStyleForAlignment(RenderStyle& styleToAdjust, const RenderStyle& parentStyle);
 
     bool m_useQuirksModeStyles;
 };
 
 } // namespace blink
 
 #endif // StyleAdjuster_h