Make RenderObject::style() return a const object

Source/core/layout/LayoutTextControlMultiLine.cpp

 /**
  * Copyright (C) 2006, 2007 Apple Inc. All rights reserved.
  *           (C) 2008 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
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 76 matching lines @@
 }
 
 LayoutObject* LayoutTextControlMultiLine::layoutSpecialExcludedChild(bool relayoutChildren, SubtreeLayoutScope& layoutScope)
 {
     LayoutObject* placeholderRenderer = LayoutTextControl::layoutSpecialExcludedChild(relayoutChildren, layoutScope);
     if (!placeholderRenderer)
         return 0;
     if (!placeholderRenderer->isBox())
         return placeholderRenderer;
     RenderBox* placeholderBox = toRenderBox(placeholderRenderer);
-    placeholderBox->style()->setLogicalWidth(Length(contentLogicalWidth() - placeholderBox->borderAndPaddingLogicalWidth(), Fixed));
+    placeholderBox->mutableStyleRef().setLogicalWidth(Length(contentLogicalWidth() - placeholderBox->borderAndPaddingLogicalWidth(), Fixed));
     placeholderBox->layoutIfNeeded();
     placeholderBox->setX(borderLeft() + paddingLeft());
     placeholderBox->setY(borderTop() + paddingTop());
     return placeholderRenderer;
 }
 
 }