Avoid double download for late discovered link preload resources.

third_party/WebKit/Source/core/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
     License as published by the Free Software Foundation; either
@@ skipping 811 matching lines @@
     if (m_preloads) {
         for (auto resource : *m_preloads) {
             if (resource->url() == url)
                 return true;
         }
     }
 
     return false;
 }
 
-void ResourceFetcher::clearPreloads()
+void ResourceFetcher::clearPreloads(ClearPreloadsType type)
 {
 #if PRELOAD_DEBUG
     printPreloadStats();
 #endif
     if (!m_preloads)
         return;
 
     for (auto resource : *m_preloads) {
         resource->decreasePreloadCount();
         bool deleted = resource->deleteIfPossible();
-        if (!deleted && resource->preloadResult() == Resource::PreloadNotReferenced)
+        if (!deleted && resource->preloadResult() == Resource::PreloadNotReferenced && (type == ClearAllPreloads || !resource->avoidBlockingOnLoad()))

[Nate Chapin, 2016/01/21 19:07:14]

I assume avoidBlockingOnLoad() is checked because that will only be set in the
rel=preload case? Maybe add a comment to explain that?

[Yoav Weiss, 2016/01/21 20:34:09]

added

             memoryCache()->remove(resource.get());
     }
     m_preloads.clear();
 }
 
 void ResourceFetcher::addAllArchiveResources(MHTMLArchive* archive)
 {
     ASSERT(archive);
     if (!m_archiveResourceCollection)
         m_archiveResourceCollection = ArchiveResourceCollection::create();
@@ skipping 303 matching lines @@
     visitor->trace(m_loaders);
     visitor->trace(m_nonBlockingLoaders);
 #if ENABLE(OILPAN)
     visitor->trace(m_documentResources);
     visitor->trace(m_preloads);
     visitor->trace(m_resourceTimingInfoMap);
 #endif
 }
 
 }