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

base/metrics/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/histogram.h"
 
 #include <limits.h>
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 38 matching lines @@
     if (allocator_) {
       ASSERT_FALSE(allocator_->IsFull());
       ASSERT_FALSE(allocator_->IsCorrupt());
     }
     UninitializeStatisticsRecorder();
     DestroyPersistentHistogramAllocator();
   }
 
   void InitializeStatisticsRecorder() {
     DCHECK(!statistics_recorder_);
-    statistics_recorder_.reset(new StatisticsRecorder());
+    statistics_recorder_ = StatisticsRecorder::CreateTemporaryForTesting();
   }
 
   void UninitializeStatisticsRecorder() {
     statistics_recorder_.reset();
   }
 
   void CreatePersistentHistogramAllocator() {
     // 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 672 matching lines @@
   // CustomHistogram needs at least 1 valid range.
   custom_ranges.clear();
   custom_ranges.push_back(0);
   EXPECT_DEATH(CustomHistogram::FactoryGet("BadRangesCustom3", custom_ranges,
                                            HistogramBase::kNoFlags),
                "");
 }
 #endif
 
 }  // namespace base