Create ForTesting method rather than declaring a dozen "friend" classes.

base/metrics/sparse_histogram_unittest.cc

 // Copyright (c) 2012 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 "base/metrics/sparse_histogram.h"
 
 #include <memory>
 #include <string>
 
 #include "base/metrics/histogram_base.h"
@@ skipping 30 matching lines @@
     if (allocator_) {
       ASSERT_FALSE(allocator_->IsFull());
       ASSERT_FALSE(allocator_->IsCorrupt());
     }
     UninitializeStatisticsRecorder();
     DestroyPersistentMemoryAllocator();
   }
 
   void InitializeStatisticsRecorder() {
     DCHECK(!statistics_recorder_);
-    statistics_recorder_.reset(new StatisticsRecorder());
+    statistics_recorder_ = StatisticsRecorder::CreateTemporaryForTesting();
   }
 
   void UninitializeStatisticsRecorder() {
     statistics_recorder_.reset();
   }
 
   void CreatePersistentMemoryAllocator() {
     // By getting the results-histogram before any persistent allocator
     // is attached, that histogram is guaranteed not to be stored in
     // any persistent memory segment (which simplifies some tests).
@@ skipping 258 matching lines @@
   TimeDelta add_ticks = TimeTicks::Now() - add_start;
   int64_t add_ms = add_ticks.InMilliseconds();
 
   VLOG(1) << kTestAddCount << " histogram adds took " << add_ms
           << "ms or about "
           << (add_ms * 1000000) / kTestAddCount
           << "ns each.";
 }
 
 }  // namespace base