Add a warning whenever link preloads are not used

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

Index: third_party/WebKit/Source/core/fetch/ResourceFetcher.cpp
diff --git a/third_party/WebKit/Source/core/fetch/ResourceFetcher.cpp b/third_party/WebKit/Source/core/fetch/ResourceFetcher.cpp
index 5ff0d0d3861a31c60532f733a76016d704734229..97affdc890cde47ef8a99006e61753eed7484276 100644
--- a/third_party/WebKit/Source/core/fetch/ResourceFetcher.cpp
+++ b/third_party/WebKit/Source/core/fetch/ResourceFetcher.cpp
@@ -906,6 +906,17 @@ void ResourceFetcher::clearPreloads(ClearPreloadsPolicy policy)
         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.