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

base/metrics/statistics_recorder_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/statistics_recorder.h"
 
 #include <stddef.h>
 
 #include <memory>
 #include <vector>
@@ skipping 29 matching lines @@
   }
 
   ~StatisticsRecorderTest() override {
     GlobalHistogramAllocator::ReleaseForTesting();
     UninitializeStatisticsRecorder();
   }
 
   void InitializeStatisticsRecorder() {
     DCHECK(!statistics_recorder_);
     StatisticsRecorder::UninitializeForTesting();
-    statistics_recorder_.reset(new StatisticsRecorder());
+    statistics_recorder_ = StatisticsRecorder::CreateTemporaryForTesting();
   }
 
   void UninitializeStatisticsRecorder() {
     statistics_recorder_.reset();
     StatisticsRecorder::UninitializeForTesting();
   }
 
   Histogram* CreateHistogram(const std::string& name,
                              HistogramBase::Sample min,
                              HistogramBase::Sample max,
@@ skipping 525 matching lines @@
   HistogramBase* histogram = Histogram::FactoryGet("TestHistogram", 1, 1000, 10,
                                                    HistogramBase::kNoFlags);
   EXPECT_TRUE(histogram);
   histogram->Add(1);
 
   EXPECT_TRUE(callback_wrapper.called);
   EXPECT_EQ(callback_wrapper.last_histogram_value, 1);
 }
 
 }  // namespace base