Add Blink support for showing image placeholders using range requests.

third_party/WebKit/Source/core/loader/ImageLoader.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2009, 2010 Apple 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 295 matching lines @@
     }
 
     if (isHTMLPictureElement(element()->parentNode()) ||
         !element()->fastGetAttribute(HTMLNames::srcsetAttr).isNull())
       resourceRequest.setRequestContext(WebURLRequest::RequestContextImageSet);
     FetchRequest request(resourceRequest, element()->localName(),
                          resourceLoaderOptions);
     configureRequest(request, bypassBehavior, *m_element,
                      document.clientHintsPreferences());
 
+    request.setPlaceholderImageRequestType(
+        updateBehavior != UpdateForcedReload && document.settings() &&
+                document.settings()->fetchImagePlaceholders()
+            ? FetchRequest::AllowPlaceholder
+            : FetchRequest::DisallowPlaceholder);
+
     newImage = ImageResource::fetch(request, document.fetcher());
 
     if (!newImage && !pageIsBeingDismissed(&document)) {
       crossSiteOrCSPViolationOccurred(imageSourceURL);
       dispatchErrorEvent();
     } else {
       clearFailedLoadURL();
     }
   } else {
     if (!imageSourceURL.isNull()) {
@@ skipping 309 matching lines @@
 }
 
 void ImageLoader::elementDidMoveToNewDocument() {
   if (m_loadDelayCounter)
     m_loadDelayCounter->documentChanged(m_element->document());
   clearFailedLoadURL();
   setImage(0);
 }
 
 }  // namespace blink