Add Blink support for showing image placeholders using range requests.

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

Index: third_party/WebKit/Source/core/css/CSSImageSetValue.cpp
diff --git a/third_party/WebKit/Source/core/css/CSSImageSetValue.cpp b/third_party/WebKit/Source/core/css/CSSImageSetValue.cpp
index 4357df9a80159457e9a3028d6f717e2b8c4068c5..99677c8cdc015297d1fbde794910d4708dc259c7 100644
--- a/third_party/WebKit/Source/core/css/CSSImageSetValue.cpp
+++ b/third_party/WebKit/Source/core/css/CSSImageSetValue.cpp
@@ -33,6 +33,7 @@
 #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"
@@ -116,6 +117,10 @@ StyleImage* CSSImageSetValue::cacheImage(
     if (crossOrigin != CrossOriginAttributeNotSet)
       request.setCrossOriginAccessControl(document.getSecurityOrigin(),
                                           crossOrigin);
+    request.setPlaceholderImageRequestType(
+        document.settings() && document.settings()->fetchImagePlaceholders()
+            ? FetchRequest::AllowPlaceholder
+            : FetchRequest::DisallowPlaceholder);
 
     if (ImageResource* cachedImage =
             ImageResource::fetch(request, document.fetcher()))