Introduce DEFINE_CONTENT_DATA_TYPE_CASTS, and use it

Source/core/css/resolver/StyleResourceLoader.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Google Inc. 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 116 matching lines @@
         case CSSPropertyBackgroundImage: {
             for (FillLayer* backgroundLayer = &style->accessBackgroundLayers(); backgroundLayer; backgroundLayer = backgroundLayer->next()) {
                 if (backgroundLayer->image() && backgroundLayer->image()->isPendingImage())
                     backgroundLayer->setImage(loadPendingImage(toStylePendingImage(backgroundLayer->image()), elementStyleResources.deviceScaleFactor()));
             }
             break;
         }
         case CSSPropertyContent: {
             for (ContentData* contentData = const_cast<ContentData*>(style->contentData()); contentData; contentData = contentData->next()) {
                 if (contentData->isImage()) {
-                    StyleImage* image = static_cast<ImageContentData*>(contentData)->image();
+                    StyleImage* image = toImageContentData(contentData)->image();
                     if (image->isPendingImage()) {
                         RefPtr<StyleImage> loadedImage = loadPendingImage(toStylePendingImage(image), elementStyleResources.deviceScaleFactor());
                         if (loadedImage)
-                            static_cast<ImageContentData*>(contentData)->setImage(loadedImage.release());
+                            toImageContentData(contentData)->setImage(loadedImage.release());
                     }
                 }
             }
             break;
         }
         case CSSPropertyCursor: {
             if (CursorList* cursorList = style->cursors()) {
                 for (size_t i = 0; i < cursorList->size(); ++i) {
                     CursorData& currentCursor = cursorList->at(i);
                     if (StyleImage* image = currentCursor.image()) {
@@ skipping 50 matching lines @@
 void StyleResourceLoader::loadPendingResources(RenderStyle* renderStyle, ElementStyleResources& elementStyleResources)
 {
     // Start loading images referenced by this style.
     loadPendingImages(renderStyle, elementStyleResources);
 
     // Start loading the SVG Documents referenced by this style.
     loadPendingSVGDocuments(renderStyle, elementStyleResources);
 }
 
 }