Constify and use reference for RenderStyle in LayoutTheme

Source/core/layout/LayoutSliderThumb.h

 /*
  * Copyright (C) 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 24 matching lines @@
 #include "core/html/shadow/SliderThumbElement.h"
 #include "core/rendering/RenderBlockFlow.h"
 
 namespace blink {
 
 class SliderThumbElement;
 
 class LayoutSliderThumb final : public RenderBlockFlow {
 public:
     LayoutSliderThumb(SliderThumbElement*);
-    void updateAppearance(RenderStyle* parentStyle);
+    void updateAppearance(const RenderStyle& parentStyle);
 
 private:
     virtual bool isOfType(RenderObjectType type) const override { return type == RenderObjectSliderThumb || RenderBlockFlow::isOfType(type); }
 };
 
 DEFINE_RENDER_OBJECT_TYPE_CASTS(LayoutSliderThumb, isSliderThumb());
 
 } // namespace blink
 
 #endif // LayoutSliderThumb_h