Make CSSValueList store const CSSValues

third_party/WebKit/Source/core/css/CSSComputedStyleDeclaration.cpp

 /*
  * Copyright (C) 2004 Zack Rusin <zack@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007 Nicholas Shanks <webkit@nickshanks.com>
  * Copyright (C) 2011 Sencha, Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
@@ skipping 548 matching lines @@
     if (forceFullLayout) {
         document.updateStyleAndLayoutIgnorePendingStylesheetsForNode(styledNode);
         styledNode = this->styledNode();
         style = computeComputedStyle();
         layoutObject = styledNode->layoutObject();
     }
 
     if (!style)
         return nullptr;
 
-    CSSValue* value = ComputedStyleCSSValueMapping::get(propertyID, *style, layoutObject, styledNode, m_allowVisitedStyle);
+    const CSSValue* value = ComputedStyleCSSValueMapping::get(propertyID, *style, layoutObject, styledNode, m_allowVisitedStyle);
     if (value)
         return value;
 
     logUnimplementedPropertyID(propertyID);
     return nullptr;
 }
 
 String CSSComputedStyleDeclaration::getPropertyValue(CSSPropertyID propertyID) const
 {
     const CSSValue* value = getPropertyCSSValue(propertyID);
@@ skipping 114 matching lines @@
     exceptionState.throwDOMException(NoModificationAllowedError, "These styles are computed, and therefore the '" + getPropertyNameString(id) + "' property is read-only.");
 }
 
 DEFINE_TRACE(CSSComputedStyleDeclaration)
 {
     visitor->trace(m_node);
     CSSStyleDeclaration::trace(visitor);
 }
 
 } // namespace blink