Remove custom counts histogram from the blink API.

third_party/WebKit/Source/core/html/parser/HTMLResourcePreloader.cpp

Index: third_party/WebKit/Source/core/html/parser/HTMLResourcePreloader.cpp
diff --git a/third_party/WebKit/Source/core/html/parser/HTMLResourcePreloader.cpp b/third_party/WebKit/Source/core/html/parser/HTMLResourcePreloader.cpp
index 91127c459a01464c991463d24e5d8459e63fe1b2..f435851cb3d5aac97e96f4abdddde04761874abf 100644
--- a/third_party/WebKit/Source/core/html/parser/HTMLResourcePreloader.cpp
+++ b/third_party/WebKit/Source/core/html/parser/HTMLResourcePreloader.cpp
@@ -29,6 +29,7 @@
 #include "core/fetch/FetchInitiatorInfo.h"
 #include "core/fetch/ResourceFetcher.h"
 #include "core/loader/DocumentLoader.h"
+#include "platform/Histogram.h"
 #include "public/platform/Platform.h"
 
 namespace blink {
@@ -75,7 +76,9 @@ void HTMLResourcePreloader::preload(PassOwnPtr<PreloadRequest> preload, const Ne
     if (preload->resourceType() == Resource::Script || preload->resourceType() == Resource::CSSStyleSheet || preload->resourceType() == Resource::ImportResource)
         request.setCharset(preload->charset().isEmpty() ? m_document->characterSet().string() : preload->charset());
     request.setForPreload(true);
-    Platform::current()->histogramCustomCounts("WebCore.PreloadDelayMs", static_cast<int>(1000 * (monotonicallyIncreasingTime() - preload->discoveryTime())), 0, 2000, 20);
+    int duration = static_cast<int>(1000 * (monotonicallyIncreasingTime() - preload->discoveryTime()));
+    DEFINE_THREAD_SAFE_STATIC_LOCAL(CustomCountHistogram, preloadDelayHistogram, new CustomCountHistogram("WebCore.PreloadDelayMs", 0, 2000, 20));

[esprehn, 2016/02/04 23:25:23]

main thread only, m_document below is only accessible from the main thread

+    preloadDelayHistogram.count(duration);
     m_document->loader()->startPreload(preload->resourceType(), request);
 }