Introduce DEFINE_CONTENT_DATA_TYPE_CASTS, and use it

Source/core/rendering/style/RenderStyle.cpp

 /*
  * Copyright (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2011 Adobe Systems Incorporated. All rights reserved.
  *
  * 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.
  *
@@ skipping 766 matching lines @@
 {
     OwnPtr<ContentData>& content = rareNonInheritedData.access()->m_content;
     if (add) {
         ContentData* lastContent = content.get();
         while (lastContent && lastContent->next())
             lastContent = lastContent->next();
 
         if (lastContent) {
             // We attempt to merge with the last ContentData if possible.
             if (lastContent->isText()) {
-                TextContentData* textContent = static_cast<TextContentData*>(lastContent);
+                TextContentData* textContent = toTextContentData(lastContent);
                 textContent->setText(textContent->text() + string);
             } else
                 lastContent->setNext(ContentData::create(string));
 
             return;
         }
     }
 
     content = ContentData::create(string);
 }
@@ skipping 889 matching lines @@
     // right
     radiiSum = radii.topRight().height() + radii.bottomRight().height();
     if (radiiSum > rect.height())
         factor = std::min(rect.height() / radiiSum, factor);
 
     ASSERT(factor <= 1);
     return factor;
 }
 
 } // namespace blink