Make RenderObject::style() return a const object

Source/core/css/CSSGradientValue.cpp

 /*
  * Copyright (C) 2008 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 50 matching lines @@
 
         // Need to look up our size.  Create a string of width*height to use as a hash key.
         Image* result = getImage(renderer, size);
         if (result)
             return result;
     }
 
     // We need to create an image.
     RefPtr<Gradient> gradient;
 
-    LayoutStyle* rootStyle = renderer->document().documentElement()->layoutStyle();
+    const LayoutStyle* rootStyle = renderer->document().documentElement()->layoutStyle();
     CSSToLengthConversionData conversionData(renderer->style(), rootStyle, renderer->view(), renderer->style()->effectiveZoom());
     if (isLinearGradientValue())
         gradient = toCSSLinearGradientValue(this)->createGradient(conversionData, size, *renderer);
     else
         gradient = toCSSRadialGradientValue(this)->createGradient(conversionData, size, *renderer);
 
     RefPtr<Image> newImage = GradientGeneratedImage::create(gradient, size);
     if (cacheable)
         putImage(size, newImage);
 
@@ skipping 1184 matching lines @@
     visitor->trace(m_firstRadius);
     visitor->trace(m_secondRadius);
     visitor->trace(m_shape);
     visitor->trace(m_sizingBehavior);
     visitor->trace(m_endHorizontalSize);
     visitor->trace(m_endVerticalSize);
     CSSGradientValue::traceAfterDispatch(visitor);
 }
 
 } // namespace blink