Make RenderObject::style() return a const object

Source/core/css/resolver/SharedStyleFinder.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (c) 2011, Code Aurora Forum. All rights reserved.
  * Copyright (C) Research In Motion Limited 2011. All rights reserved.
@@ skipping 180 matching lines @@
             return false;
     }
     return true;
 }
 
 bool SharedStyleFinder::canShareStyleWithElement(Element& candidate) const
 {
     if (element() == candidate)
         return false;
     Element* parent = candidate.parentOrShadowHostElement();
-    LayoutStyle* style = candidate.layoutStyle();
+    const LayoutStyle* style = candidate.layoutStyle();
     if (!style)
         return false;
     if (!style->isSharable())
         return false;
     if (!parent)
         return false;
     if (element().parentOrShadowHostElement()->layoutStyle() != parent->layoutStyle())
         return false;
     if (candidate.tagQName() != element().tagQName())
         return false;
@@ skipping 125 matching lines @@
         INCREMENT_STYLE_STATS_COUNTER(m_styleResolver, sharedStyleRejectedByUncommonAttributeRules);
         return 0;
     }
 
     // Tracking child index requires unique style for each node. This may get set by the sibling rule match above.
     if (!element().parentElementOrShadowRoot()->childrenSupportStyleSharing()) {
         INCREMENT_STYLE_STATS_COUNTER(m_styleResolver, sharedStyleRejectedByParent);
         return 0;
     }
 
-    return shareElement->layoutStyle();
+    return shareElement->mutableLayoutStyle();
 }
 
 }