Use lock-free lazy initialization for static histogram references

chrome/browser/extensions/extension_metrics_module.cc

 // Copyright (c) 2010 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 "chrome/browser/extensions/extension_metrics_module.h"
 
 #include "base/metrics/histogram.h"
 #include "base/values.h"
 #include "chrome/common/extensions/extension.h"
 #include "chrome/browser/metrics/user_metrics.h"
@@ skipping 57 matching lines @@
   return true;
 }
 
 bool MetricsHistogramHelperFunction::RecordValue(const std::string& name,
                                                  Histogram::ClassType type,
                                                  int min,
                                                  int max,
                                                  size_t buckets,
                                                  int sample) {
   std::string full_name = BuildMetricName(name, GetExtension());
-  scoped_refptr<Histogram> counter;
+  Histogram* counter;
   if (type == Histogram::LINEAR_HISTOGRAM) {
     counter = LinearHistogram::FactoryGet(full_name,
                                           min,
                                           max,
                                           buckets,
                                           Histogram::kUmaTargetedHistogramFlag);
   } else {
     counter = Histogram::FactoryGet(full_name,
                                     min,
                                     max,
@@ skipping 73 matching lines @@
   return RecordValue(name, Histogram::HISTOGRAM, 1, kThreeMinMs, 50, sample);
 }
 
 bool MetricsRecordLongTimeFunction::RunImpl() {
   std::string name;
   int sample;
   EXTENSION_FUNCTION_VALIDATE(GetNameAndSample(&name, &sample));
   static const int kOneHourMs = 60 * 60 * 1000;
   return RecordValue(name, Histogram::HISTOGRAM, 1, kOneHourMs, 50, sample);
 }