Add Blink support for showing image placeholders using range requests.

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

Index: third_party/WebKit/Source/core/loader/DocumentLoader.cpp
diff --git a/third_party/WebKit/Source/core/loader/DocumentLoader.cpp b/third_party/WebKit/Source/core/loader/DocumentLoader.cpp
index 7f689758f73ce58cb90169608e096f5f9c89130e..621a5627f18deb2ba419cd0a67d96b3344ec31cd 100644
--- a/third_party/WebKit/Source/core/loader/DocumentLoader.cpp
+++ b/third_party/WebKit/Source/core/loader/DocumentLoader.cpp
@@ -163,6 +163,12 @@ Resource* DocumentLoader::startPreload(Resource::Type type,
   Resource* resource = nullptr;
   switch (type) {
     case Resource::Image:
+      request.setPlaceholderImageRequestType(
+          m_frame && m_frame->settings() &&
+                  m_frame->settings()->fetchImagePlaceholders()
+              ? FetchRequest::AllowPlaceholder
+              : FetchRequest::DisallowPlaceholder);
+
       resource = ImageResource::fetch(request, fetcher());
       break;
     case Resource::Script: