Removal of rel=preload link elements should stop the download.

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

 /*
  * Copyright (C) 2011 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 264 matching lines @@
 
     // TODO(yoav): Convert all uses of the CrossOriginAttribute to CrossOriginAttributeValue. crbug.com/486689
     // FIXME(crbug.com/463266): We're ignoring type here. Maybe we shouldn't.
     dnsPrefetchIfNeeded(relAttribute, href, document, networkHintsInterface, LinkCalledFromMarkup);
 
     preconnectIfNeeded(relAttribute, href, document, crossOrigin, networkHintsInterface, LinkCalledFromMarkup);
 
     if (m_client->shouldLoadLink())
         createLinkPreloadResourceClient(preloadIfNeeded(relAttribute, href, document, as, LinkCalledFromMarkup));
 
+    if (href.isEmpty() || !href.isValid())
+        released();
+
     // FIXME(crbug.com/323096): Should take care of import.
     if ((relAttribute.isLinkPrefetch() || relAttribute.isLinkSubresource()) && href.isValid() && document.frame()) {
         if (!m_client->shouldLoadLink())
             return false;
         Resource::Type type = Resource::LinkPrefetch;
         if (relAttribute.isLinkSubresource()) {
             type = Resource::LinkSubresource;
             UseCounter::count(document, UseCounter::LinkRelSubresource);
         } else {
             UseCounter::count(document, UseCounter::LinkRelPrefetch);
@@ skipping 21 matching lines @@
 }
 
 void LinkLoader::released()
 {
     // Only prerenders need treatment here; other links either use the Resource interface, or are notionally
     // atomic (dns prefetch).
     if (m_prerender) {
         m_prerender->cancel();
         m_prerender.clear();
     }
+    if (m_linkPreloadResourceClient)
+        m_linkPreloadResourceClient->clear();

[Nate Chapin, 2016/01/21 21:53:17]

I had actually meant deleting the LinkPreloadResourceClient, which should
implicitly call clearResource(). Sorry for not being more clear.

 }
 
 DEFINE_TRACE(LinkLoader)
 {
     visitor->trace(m_client);
     visitor->trace(m_prerender);
     visitor->trace(m_linkPreloadResourceClient);
     ResourceOwner<Resource, ResourceClient>::trace(visitor);
 }
 
 }