Introduce DEFINE_CONTENT_DATA_TYPE_CASTS, and use it

Source/core/rendering/RenderObject.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 140 matching lines @@
     // Minimal support for content properties replacing an entire element.
     // Works only if we have exactly one piece of content and it's a URL.
     // Otherwise acts as if we didn't support this feature.
     const ContentData* contentData = style->contentData();
     if (contentData && !contentData->next() && contentData->isImage() && !element->isPseudoElement()) {
         RenderImage* image = new RenderImage(element);
         // RenderImageResourceStyleImage requires a style being present on the image but we don't want to
         // trigger a style change now as the node is not fully attached. Moving this code to style change
         // doesn't make sense as it should be run once at renderer creation.
         image->setStyleInternal(style);
-        if (const StyleImage* styleImage = static_cast<const ImageContentData*>(contentData)->image()) {
+        if (const StyleImage* styleImage = toImageContentData(contentData)->image()) {
             image->setImageResource(RenderImageResourceStyleImage::create(const_cast<StyleImage*>(styleImage)));
             image->setIsGeneratedContent();
         } else
             image->setImageResource(RenderImageResource::create());
         image->setStyleInternal(nullptr);
         return image;
     }
 
     switch (style->display()) {
     case NONE:
@@ skipping 3273 matching lines @@
 {
     if (object1) {
         const blink::RenderObject* root = object1;
         while (root->parent())
             root = root->parent();
         root->showRenderTreeAndMark(object1, "*", object2, "-", 0);
     }
 }
 
 #endif