Make RenderObject::style() return a const object

Source/core/dom/Node.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004-2011, 2014 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * 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
@@ skipping 526 matching lines @@
     bool inDetach() const;
 #endif
 
     void reattach(const AttachContext& = AttachContext());
     void lazyReattachIfAttached();
 
     // Returns true if recalcStyle should be called on the object, if there is such a method (on Document and Element).
     bool shouldCallRecalcStyle(StyleRecalcChange);
 
     // Wrapper for nodes that don't have a renderer, but still cache the style (like HTMLOptionElement).
-    LayoutStyle* layoutStyle() const;
-    LayoutStyle* parentLayoutStyle() const;
+    const LayoutStyle* layoutStyle() const;
+    LayoutStyle* mutableLayoutStyle() const;
+    const LayoutStyle* parentLayoutStyle() const;
 
     const LayoutStyle& layoutStyleRef() const;
 
     LayoutStyle* computedStyle(PseudoId pseudoElementSpecifier = NOPSEUDO) { return virtualComputedStyle(pseudoElementSpecifier); }
 
     // -----------------------------------------------------------------------------
     // Notification of document structure changes (see ContainerNode.h for more notification methods)
     //
     // At first, WebKit notifies the node that it has been inserted into the document. This is called during document parsing, and also
     // when a node is added through the DOM methods insertBefore(), appendChild() or replaceChild(). The call happens _after_ the node has been added to the tree.
@@ skipping 346 matching lines @@
 } // namespace blink
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showNode(const blink::Node*);
 void showTree(const blink::Node*);
 void showNodePath(const blink::Node*);
 #endif
 
 #endif // Node_h