Avoid double download for late discovered link preload resources.

third_party/WebKit/Source/core/fetch/ResourceFetcher.h

 /*
     Copyright (C) 1998 Lars Knoll (knoll@mpi-hd.mpg.de)
     Copyright (C) 2001 Dirk Mueller <mueller@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
     version 2 of the License, or (at your option) any later version.
@@ skipping 75 matching lines @@
 
     void setImagesEnabled(bool);
 
     bool shouldDeferImageLoad(const KURL&) const;
 
     FetchContext& context() const { return m_context ? *m_context.get() : FetchContext::nullInstance(); }
     void clearContext() { m_context.clear(); }
 
     int requestCount() const;
 
+    enum ClearPreloadsPolicy { ClearAllPreloads, ClearSpeculativeMarkupPreloads };
+
     bool isPreloaded(const KURL&) const;
-    void clearPreloads();
+    void clearPreloads(ClearPreloadsPolicy = ClearAllPreloads);
     void preloadStarted(Resource*);
     void printPreloadStats();
 
     void addAllArchiveResources(MHTMLArchive*);
     ArchiveResourceCollection* archiveResourceCollection() const { return m_archiveResourceCollection.get(); }
 
     void setDefersLoading(bool);
     void stopFetching();
     bool isFetching() const;
 
@@ skipping 139 matching lines @@
             m_loader->m_allowStaleResources = m_previousState;
     }
 private:
     Member<ResourceFetcher> m_loader;
     bool m_previousState;
 };
 
 } // namespace blink
 
 #endif // ResourceFetcher_h