Use lock-free lazy initialization for static histogram references

net/disk_cache/stats_histogram.h

-// Copyright (c) 2008 The Chromium Authors. All rights reserved.
+// 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.
 
 #ifndef NET_DISK_CACHE_STATS_HISTOGRAM_H_
 #define NET_DISK_CACHE_STATS_HISTOGRAM_H_
 #pragma once
 
 #include <string>
 
 #include "base/metrics/histogram.h"
@@ skipping 16 matching lines @@
     Counts* GetCounts() {
       return &counts_;
     }
   };
 
   explicit StatsHistogram(const std::string& name, Sample minimum,
                           Sample maximum, size_t bucket_count)
       : Histogram(name, minimum, maximum, bucket_count), init_(false) {}
   ~StatsHistogram();
 
-  static scoped_refptr<StatsHistogram>
-      StatsHistogramFactoryGet(const std::string& name);
+  static StatsHistogram* StatsHistogramFactoryGet(const std::string& name);
 
   // We'll be reporting data from the given set of cache stats.
   bool Init(const Stats* stats);
 
   virtual Sample ranges(size_t i) const;
   virtual size_t bucket_count() const;
   virtual void SnapshotSample(SampleSet* sample) const;
   virtual Inconsistencies FindCorruption(const SampleSet& snapshot) const;
   virtual uint32 CalculateRangeChecksum() const;
 
  private:
   bool init_;
   static const Stats* stats_;
   DISALLOW_COPY_AND_ASSIGN(StatsHistogram);
 };
 
 }  // namespace disk_cache
 
 #endif  // NET_DISK_CACHE_STATS_HISTOGRAM_H_