Add histograms to ResourceFetcher to evaluate memory cache hit rate

Source/core/fetch/ResourceFetcher.cpp

Index: Source/core/fetch/ResourceFetcher.cpp
diff --git a/Source/core/fetch/ResourceFetcher.cpp b/Source/core/fetch/ResourceFetcher.cpp
index b79496ad978b14ac2c5678920b110412760b29fe..f21d2ff44b0204f039f8db6e6cf9bfcda4d5bae7 100644
--- a/Source/core/fetch/ResourceFetcher.cpp
+++ b/Source/core/fetch/ResourceFetcher.cpp
@@ -225,6 +225,9 @@ ResourceFetcher::ResourceFetcher(DocumentLoader* documentLoader)
     , m_requestCount(0)
     , m_garbageCollectDocumentResourcesTimer(this, &ResourceFetcher::garbageCollectDocumentResourcesTimerFired)
     , m_resourceTimingReportTimer(this, &ResourceFetcher::resourceTimingReportTimerFired)
+    , m_useCount(0)
+    , m_revalidateCount(0)
+    , m_loadCount(0)
     , m_autoLoadImages(true)
     , m_imagesEnabled(true)
     , m_allowStaleResources(false)
@@ -238,6 +241,13 @@ ResourceFetcher::~ResourceFetcher()
 
     clearPreloads();
 
+    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);
+
     // Make sure no requests still point to this ResourceFetcher
     ASSERT(!m_requestCount);
 }
@@ -629,13 +639,18 @@ ResourcePtr<Resource> ResourceFetcher::requestResource(Resource::Type type, Fetc
         // Fall through
     case Load:
         resource = loadResource(type, request, request.charset());
+        ++m_loadCount;

[Nate Chapin, 2014/01/28 20:22:54]

Would it be cleaner to wrap these variables up into a simple helper class owner
by ResourceFetcher?

I'd at least prefer that incrementing the appropriate counter be done in a
helper function, rather than in this switch statement.

[clamy, 2014/01/29 12:19:21]

Done.

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