Add a warning whenever link preloads are not used

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

Index: third_party/WebKit/Source/core/fetch/ResourceFetcher.h
diff --git a/third_party/WebKit/Source/core/fetch/ResourceFetcher.h b/third_party/WebKit/Source/core/fetch/ResourceFetcher.h
index 52a02be8f15623feede02887e52c5cd9037e0f6c..4150394a57dca6aa3e076ef0af11a826cbe7dc22 100644
--- a/third_party/WebKit/Source/core/fetch/ResourceFetcher.h
+++ b/third_party/WebKit/Source/core/fetch/ResourceFetcher.h
@@ -98,9 +98,11 @@ public:
     bool isPreloadedForTest(const KURL&) const;
 
     int countPreloads() const { return m_preloads ? m_preloads->size() : 0; }
+    bool hasUnusedLinkPreloads() { return m_unusedLinkPreloadCounter > 0; }
     void clearPreloads(ClearPreloadsPolicy = ClearAllPreloads);
     void preloadStarted(Resource*);
     void logPreloadStats();
+    void warnUnusedPreloads();
 
     MHTMLArchive* archive() const { return m_archive.get(); }
     ArchiveResource* createArchive(Resource*);
@@ -182,6 +184,7 @@ private:
     mutable DocumentResourceMap m_documentResources;
 
     Member<HeapListHashSet<Member<Resource>>> m_preloads;
+    unsigned m_unusedLinkPreloadCounter;
     Member<MHTMLArchive> m_archive;
 
     Timer<ResourceFetcher> m_resourceTimingReportTimer;