Add a warning whenever link preloads are not used

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 888 matching lines @@
             resource->decreasePreloadCount();
             if (resource->getPreloadResult() == Resource::PreloadNotReferenced)
                 memoryCache()->remove(resource.get());
             m_preloads->remove(resource);
         }
     }
     if (!m_preloads->size())
         m_preloads.clear();
 }
 
+void ResourceFetcher::warnUnusedPreloads()
+{
+    if (!m_preloads)
+        return;
+    for (auto resource : *m_preloads) {

[Charlie Harrison, 2016/09/14 12:34:58]

const auto& ?

[Yoav Weiss, 2016/09/14 13:28:31]

Yeah. I'll also modify all the other iterations of m_preloads in the file.

+        if (resource && resource->isLinkPreload() && resource->getPreloadResult() == Resource::PreloadNotReferenced) {
+            context().addConsoleMessage("The resource " + resource->url().getString() + " was preloaded but not used within a few seconds from the window's load event. Please make sure it wasn't preloaded for nothing.", WarningMessageLevel);

[Charlie Harrison, 2016/09/14 12:34:58]

Do you think you should include the fact that it was a link preload or do you
think it's obvious?

[Yoav Weiss, 2016/09/14 13:28:31]

nothing is obvious :) I'll add it to the comment

+        }
+    }
+}
+
 ArchiveResource* ResourceFetcher::createArchive(Resource* resource)
 {
     // Only the top-frame can load MHTML.
     if (!context().isMainFrame())
         return nullptr;
     m_archive = MHTMLArchive::create(resource->url(), resource->resourceBuffer());
     return m_archive ? m_archive->mainResource() : nullptr;
 }
 
 void ResourceFetcher::didFinishLoading(Resource* resource, double finishTime, int64_t encodedDataLength, DidFinishLoadingReason finishReason)
@@ skipping 404 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