Use lock-free lazy initialization for static histogram references

chrome/browser/extensions/extension_metrics_apitest.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <map>
 
 #include "base/metrics/histogram.h"
 #include "chrome/browser/extensions/extension_apitest.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/extensions/extension.h"
@@ skipping 105 matching lines @@
   // Code other than the tests tun here will record some histogram values, but
   // we will ignore those. This function validates that all the histogram we
   // expect to see are present in the list, and that their basic info is
   // correct.
   for (int i = 0; i < count; ++i) {
     const RecordedHistogram& r = recorded[i];
     std::string name(BuildFullName(r.name, extension));
 
     size_t j = 0;
     for (j = 0; j < histograms.size(); ++j) {
-      scoped_refptr<base::Histogram> histogram(histograms[j]);
+      base::Histogram* histogram(histograms[j]);
 
       if (name == histogram->histogram_name()) {
         EXPECT_EQ(r.type, histogram->histogram_type());
         EXPECT_EQ(r.min, histogram->declared_min());
         EXPECT_EQ(r.max, histogram->declared_max());
         EXPECT_EQ(r.buckets, histogram->bucket_count());
         break;
       }
     }
     EXPECT_LT(j, histograms.size());
@@ skipping 10 matching lines @@
 
   ASSERT_TRUE(RunExtensionTest("metrics")) << message_;
   const Extension* extension = GetSingleLoadedExtension();
   ASSERT_TRUE(extension);
 
   observer.ValidateUserActions(extension,
                                g_user_actions,
                                arraysize(g_user_actions));
   ValidateHistograms(extension, g_histograms, arraysize(g_histograms));
 }