Handle main resource preload request better

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 737 matching lines @@
             if (memoryCache()->contains(resource.get()))
                 memoryCache()->remove(resource.get());
             return request.options().synchronousPolicy == RequestSynchronously ? resource : 0;
         }
     }
 
     // FIXME: Temporarily leave main resource caching disabled for chromium,
     // see https://bugs.webkit.org/show_bug.cgi?id=107962. Before caching main
     // resources, we should be sure to understand the implications for memory
     // use.
-    //
-    // Ensure main resources aren't preloaded, and other main resource loads
-    // are removed from cache to prevent reuse.
+    // Remove main resource from cache to prevent reuse.
     if (type == Resource::MainResource) {
         ASSERT(policy != Use || m_documentLoader->substituteData().isValid());
         ASSERT(policy != Revalidate);
         memoryCache()->remove(resource.get());
-        if (request.forPreload())
-            return 0;
     }
 
     requestLoadStarted(resource.get(), request, policy == Use ? ResourceLoadingFromCache : ResourceLoadingFromNetwork);
 
     ASSERT(resource->url() == url.string());
     m_documentResources.set(resource->url(), resource);
     return resource;
 }
 
 void ResourceFetcher::resourceTimingReportTimerFired(Timer<ResourceFetcher>* timer)
@@ skipping 413 matching lines @@
     ASSERT(m_requestCount > -1);
 }
 
 void ResourceFetcher::preload(Resource::Type type, FetchRequest& request, const String& charset)
 {
     requestPreload(type, request, charset);
 }
 
 void ResourceFetcher::requestPreload(Resource::Type type, FetchRequest& request, const String& charset)
 {
+    // Ensure main resources aren't preloaded, since the cache can't actually reuse the preload.
+    if (type == Resource::MainResource)
+        return;
+
     String encoding;
     if (type == Resource::Script || type == Resource::CSSStyleSheet)
         encoding = charset.isEmpty() ? m_document->charset().string() : charset;
 
     request.setCharset(encoding);
     request.setForPreload(true);
 
     ResourcePtr<Resource> resource = requestResource(type, request);
     if (!resource || (m_preloads && m_preloads->contains(resource.get())))
         return;
@@ skipping 282 matching lines @@
     }
 }
 
 void ResourceFetcher::trace(Visitor* visitor)
 {
     visitor->trace(m_document);
     ResourceLoaderHost::trace(visitor);
 }
 
 }