Add histograms to ResourceFetcher to evaluate memory cache hit rate

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 203 matching lines @@
     Timer<ResourceFetcher> m_resourceTimingReportTimer;
 
     typedef HashMap<Resource*, RefPtr<ResourceTimingInfo> > ResourceTimingInfoMap;
     ResourceTimingInfoMap m_resourceTimingInfoMap;
 
     HashMap<RefPtr<ResourceTimingInfo>, bool> m_scheduledResourceTimingReports;
 
     OwnPtr<ResourceLoaderSet> m_loaders;
     OwnPtr<ResourceLoaderSet> m_multipartLoaders;
 
+    // Used in hit rate histograms.
+    class DeadResourceStatsRecorder {
+    public:
+        DeadResourceStatsRecorder();
+        ~DeadResourceStatsRecorder();
+
+        void update(RevalidationPolicy);
+
+    private:
+        int m_useCount;
+        int m_revalidateCount;
+        int m_loadCount;
+    };
+    DeadResourceStatsRecorder m_deadStatsRecorder;
+
     // 29 bits left
     bool m_autoLoadImages : 1;
     bool m_imagesEnabled : 1;
     bool m_allowStaleResources : 1;
 };
 
 class ResourceCacheValidationSuppressor {
     WTF_MAKE_NONCOPYABLE(ResourceCacheValidationSuppressor);
     WTF_MAKE_FAST_ALLOCATED;
 public:
@@ skipping 12 matching lines @@
             m_loader->m_allowStaleResources = m_previousState;
     }
 private:
     ResourceFetcher* m_loader;
     bool m_previousState;
 };
 
 } // namespace WebCore
 
 #endif