Add Blink support for showing image placeholders using range requests.

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

 /*
  * Copyright (C) 2012 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 15 matching lines @@
 #include "core/css/CSSImageSetValue.h"
 
 #include "core/css/CSSImageValue.h"
 #include "core/css/CSSPrimitiveValue.h"
 #include "core/dom/Document.h"
 #include "core/fetch/FetchInitiatorTypeNames.h"
 #include "core/fetch/FetchRequest.h"
 #include "core/fetch/ImageResource.h"
 #include "core/fetch/ResourceFetcher.h"
 #include "core/fetch/ResourceLoaderOptions.h"
+#include "core/frame/Settings.h"
 #include "core/style/StyleFetchedImageSet.h"
 #include "core/style/StyleInvalidImage.h"
 #include "platform/weborigin/KURL.h"
 #include "platform/weborigin/SecurityPolicy.h"
 #include "wtf/text/StringBuilder.h"
 #include <algorithm>
 
 namespace blink {
 
 CSSImageSetValue::CSSImageSetValue()
@@ skipping 63 matching lines @@
     // Page::pageScaleFactor(), LocalFrame::pageZoomFactor(), and any CSS
     // transforms. https://bugs.webkit.org/show_bug.cgi?id=81698
     ImageWithScale image = bestImageForScaleFactor(deviceScaleFactor);
     FetchRequest request(ResourceRequest(document.completeURL(image.imageURL)),
                          FetchInitiatorTypeNames::css);
     request.mutableResourceRequest().setHTTPReferrer(image.referrer);
 
     if (crossOrigin != CrossOriginAttributeNotSet)
       request.setCrossOriginAccessControl(document.getSecurityOrigin(),
                                           crossOrigin);
+    if (document.settings() && document.settings()->fetchImagePlaceholders())
+      request.setAllowImagePlaceholder();
 
     if (ImageResource* cachedImage =
             ImageResource::fetch(request, document.fetcher()))
       m_cachedImage = StyleFetchedImageSet::create(
           cachedImage, image.scaleFactor, this, request.url());
     else
       m_cachedImage = StyleInvalidImage::create(image.imageURL);
     m_cachedScaleFactor = deviceScaleFactor;
   }
 
@@ skipping 46 matching lines @@
 CSSImageSetValue* CSSImageSetValue::valueWithURLsMadeAbsolute() {
   CSSImageSetValue* value = CSSImageSetValue::create();
   for (auto& item : *this)
     item->isImageValue()
         ? value->append(*toCSSImageValue(*item).valueWithURLMadeAbsolute())
         : value->append(*item);
   return value;
 }
 
 }  // namespace blink