Do not treat substitute-data resources as having successful HTTP status codes.

third_party/WebKit/Source/platform/loader/fetch/ResourceFetcher.cpp

 /*
     Copyright (C) 1998 Lars Knoll (knoll@mpi-hd.mpg.de)
     Copyright (C) 2001 Dirk Mueller (mueller@kde.org)
     Copyright (C) 2002 Waldo Bastian (bastian@kde.org)
     Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All
     rights reserved.
     Copyright (C) 2009 Torch Mobile Inc. http://www.torchmobile.com/
 
     This library is free software; you can redistribute it and/or
     modify it under the terms of the GNU Library General Public
@@ skipping 365 matching lines @@
         m_archive->subresourceForURL(request.url());
     // Fall back to the network if the archive doesn't contain the resource.
     if (!archiveResource)
       return nullptr;
     mimetype = archiveResource->mimeType();
     charset = archiveResource->textEncoding();
     data = archiveResource->data();
   }
 
   ResourceResponse response(url, mimetype, data->size(), charset, String());
-  response.setHTTPStatusCode(200);

[Nate Chapin, 2017/02/03 18:00:22]

This also means data: urls won't have status code. I assume that's ok?

-  response.setHTTPStatusText("OK");
 
   Resource* resource = factory.create(request.resourceRequest(),
                                       request.options(), request.charset());
   resource->setNeedsSynchronousCacheHit(substituteData.forceSynchronousLoad());
   // FIXME: We should provide a body stream here.
   resource->responseReceived(response, nullptr);
   resource->setDataBufferingPolicy(BufferData);
   if (data->size())
     resource->setResourceBuffer(data);
   resource->setIdentifier(createUniqueIdentifier());
@@ skipping 1127 matching lines @@
   visitor->trace(m_context);
   visitor->trace(m_archive);
   visitor->trace(m_loaders);
   visitor->trace(m_nonBlockingLoaders);
   visitor->trace(m_documentResources);
   visitor->trace(m_preloads);
   visitor->trace(m_resourceTimingInfoMap);
 }
 
 }  // namespace blink