Add UMA to track time between preload discovery and reference

third_party/WebKit/Source/core/fetch/Resource.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) 2006 Samuel Weinig (sam.weinig@gmail.com)
     Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
 
     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 14 matching lines @@
 
 #include "core/fetch/CachedMetadata.h"
 #include "core/fetch/CrossOriginAccessControl.h"
 #include "core/fetch/FetchInitiatorTypeNames.h"
 #include "core/fetch/MemoryCache.h"
 #include "core/fetch/ResourceClient.h"
 #include "core/fetch/ResourceClientOrObserverWalker.h"
 #include "core/fetch/ResourceFetcher.h"
 #include "core/fetch/ResourceLoader.h"
 #include "core/inspector/InstanceCounters.h"
+#include "platform/Histogram.h"
 #include "platform/Logging.h"
 #include "platform/SharedBuffer.h"
 #include "platform/TraceEvent.h"
 #include "platform/network/HTTPParsers.h"
 #include "platform/weborigin/KURL.h"
 #include "public/platform/Platform.h"
 #include "public/platform/WebScheduler.h"
 #include "public/platform/WebSecurityOrigin.h"
 #include "wtf/CurrentTime.h"
 #include "wtf/MathExtras.h"
@@ skipping 250 matching lines @@
     : m_resourceRequest(request)
     , m_options(options)
     , m_responseTimestamp(currentTime())
     , m_cancelTimer(this, &Resource::cancelTimerFired)
     , m_loadFinishTime(0)
     , m_identifier(0)
     , m_encodedSize(0)
     , m_decodedSize(0)
     , m_overheadSize(calculateOverheadSize())
     , m_preloadCount(0)
+    , m_preloadDiscoveryTime(0.0)
     , m_cacheIdentifier(MemoryCache::defaultCacheIdentifier())
     , m_preloadResult(PreloadNotReferenced)
     , m_type(type)
     , m_status(NotStarted)
     , m_needsSynchronousCacheHit(false)
     , m_linkPreload(false)
 {
     ASSERT(m_type == unsigned(type)); // m_type is a bitfield, so this tests careless updates of the enum.
     InstanceCounters::incrementCounter(InstanceCounters::ResourceCounter);
 
@@ skipping 362 matching lines @@
 void Resource::willAddClientOrObserver()
 {
     ASSERT(!isPurgeable());
     if (m_preloadResult == PreloadNotReferenced) {
         if (isLoaded())
             m_preloadResult = PreloadReferencedWhileComplete;
         else if (isLoading())
             m_preloadResult = PreloadReferencedWhileLoading;
         else
             m_preloadResult = PreloadReferenced;
+
+        if (m_preloadDiscoveryTime) {
+            int timeSinceDiscovery = static_cast<int>(1000 * (monotonicallyIncreasingTime() - m_preloadDiscoveryTime));
+            DEFINE_STATIC_LOCAL(CustomCountHistogram, preloadDiscoveryHistogram, ("PreloadScanner.ReferenceTime", 0, 10000, 50));
+            preloadDiscoveryHistogram.count(timeSinceDiscovery);
+        }
     }
     if (!hasClientsOrObservers())
         memoryCache()->makeLive(this);
 }
 
 void Resource::addClient(ResourceClient* client)
 {
     willAddClientOrObserver();
 
     if (!m_revalidatingRequest.isNull()) {
@@ skipping 424 matching lines @@
     case Resource::Media:
         return "Media";
     case Resource::Manifest:
         return "Manifest";
     }
     ASSERT_NOT_REACHED();
     return "Unknown";
 }
 
 } // namespace blink