Make RenderObject::style() return a const object

Source/core/layout/LayoutSliderThumb.cpp

 /*
  * 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 27 matching lines @@
 namespace blink {
 
 LayoutSliderThumb::LayoutSliderThumb(SliderThumbElement* element)
     : RenderBlockFlow(element)
 {
 }
 
 void LayoutSliderThumb::updateAppearance(const LayoutStyle& parentStyle)
 {
     if (parentStyle.appearance() == SliderVerticalPart)
-        style()->setAppearance(SliderThumbVerticalPart);
+        mutableStyleRef().setAppearance(SliderThumbVerticalPart);
     else if (parentStyle.appearance() == SliderHorizontalPart)
-        style()->setAppearance(SliderThumbHorizontalPart);
+        mutableStyleRef().setAppearance(SliderThumbHorizontalPart);
     else if (parentStyle.appearance() == MediaSliderPart)
-        style()->setAppearance(MediaSliderThumbPart);
+        mutableStyleRef().setAppearance(MediaSliderThumbPart);
     else if (parentStyle.appearance() == MediaVolumeSliderPart)
-        style()->setAppearance(MediaVolumeSliderThumbPart);
+        mutableStyleRef().setAppearance(MediaVolumeSliderThumbPart);
     else if (parentStyle.appearance() == MediaFullScreenVolumeSliderPart)
-        style()->setAppearance(MediaFullScreenVolumeSliderThumbPart);
+        mutableStyleRef().setAppearance(MediaFullScreenVolumeSliderThumbPart);
     if (style()->hasAppearance())
         LayoutTheme::theme().adjustSliderThumbSize(mutableStyleRef(), toElement(node()));
 }
 
 } // namespace blink