Add histograms to ResourceFetcher to evaluate memory cache hit rate

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 614 matching lines @@
         break;
     case Revalidate:
         resource = revalidateResource(request, resource.get());
         break;
     case Use:
         resource->updateForAccess();
         notifyLoadedFromMemoryCache(resource.get());
         break;
     }
 
+    if (!resource->hasClients())

[Nate Chapin, 2014/01/29 18:19:56]

We null-check resource just below this. Either this should be after the
null-check, or we should remove the null-check. I'm pretty sure it's
unnecessary.

+        m_deadStatsRecorder.update(policy);
+
     if (!resource)
         return 0;
 
     if (policy != Use)
         resource->setIdentifier(createUniqueIdentifier());
 
     if (!request.forPreload() || policy != Use) {
         ResourceLoadPriority priority = loadPriority(type, request);
         if (priority != resource->resourceRequest().priority()) {
             resource->resourceRequest().setPriority(priority);
@@ skipping 721 matching lines @@
         printf("IMAGES:  %d (%d hits, hit rate %d%%)\n", images, images - imageMisses, (images - imageMisses) * 100 / images);
 }
 #endif
 
 const ResourceLoaderOptions& ResourceFetcher::defaultResourceOptions()
 {
     DEFINE_STATIC_LOCAL(ResourceLoaderOptions, options, (SniffContent, BufferData, AllowStoredCredentials, ClientRequestedCredentials, AskClientForCrossOriginCredentials, DoSecurityCheck, CheckContentSecurityPolicy, DocumentContext));
     return options;
 }
 
+ResourceFetcher::DeadResourceStatsRecorder::DeadResourceStatsRecorder()
+    : m_useCount(0)
+    , m_revalidateCount(0)
+    , m_loadCount(0)
+{
 }
+
+ResourceFetcher::DeadResourceStatsRecorder::~DeadResourceStatsRecorder()
+{
+    blink::Platform::current()->histogramCustomCounts(
+        "WebCore.ResourceFetcher.HitCount", m_useCount, 0, 1000, 50);
+    blink::Platform::current()->histogramCustomCounts(
+        "WebCore.ResourceFetcher.RevalidateCount", m_revalidateCount, 0, 1000, 50);
+    blink::Platform::current()->histogramCustomCounts(
+        "WebCore.ResourceFetcher.LoadCount", m_loadCount, 0, 1000, 50);
+}
+
+void ResourceFetcher::DeadResourceStatsRecorder::update(RevalidationPolicy policy)
+{
+    switch (policy) {
+    case Reload:
+        // Fall through.

[Nate Chapin, 2014/01/29 18:19:56]

Given that Reload and Load cases are identical, this comment probably isn't
necessary.

+    case Load:
+        ++m_loadCount;
+        break;

[Nate Chapin, 2014/01/29 18:19:56]

return instead?

+    case Revalidate:
+        ++m_revalidateCount;
+        break;
+    case Use:
+        ++m_useCount;
+        break;
+    }
+}
+
+}