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

base/metrics/histogram_snapshot_manager_unittest.cc

 // Copyright 2014 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_snapshot_manager.h"
 
 #include <string>
 #include <vector>
 
 #include "base/macros.h"
@@ skipping 50 matching lines @@
  private:
   std::vector<std::string> recorded_delta_histogram_names_;
   std::map<std::string, int64_t> recorded_delta_histogram_sum_;
 
   DISALLOW_COPY_AND_ASSIGN(HistogramFlattenerDeltaRecorder);
 };
 
 class HistogramSnapshotManagerTest : public testing::Test {
  protected:
   HistogramSnapshotManagerTest()
-      : histogram_snapshot_manager_(&histogram_flattener_delta_recorder_) {}
+      : statistics_recorder_(StatisticsRecorder::CreateTemporaryForTesting()),
+        histogram_snapshot_manager_(&histogram_flattener_delta_recorder_) {}
 
   ~HistogramSnapshotManagerTest() override {}
 
-  StatisticsRecorder statistics_recorder_;
+  std::unique_ptr<StatisticsRecorder> statistics_recorder_;
   HistogramFlattenerDeltaRecorder histogram_flattener_delta_recorder_;
   HistogramSnapshotManager histogram_snapshot_manager_;
 };
 
 TEST_F(HistogramSnapshotManagerTest, PrepareDeltasNoFlagsFilter) {
   // kNoFlags filter should record all histograms.
   UMA_HISTOGRAM_ENUMERATION("UmaHistogram", 1, 4);
   UMA_STABILITY_HISTOGRAM_ENUMERATION("UmaStabilityHistogram", 1, 2);
 
   histogram_snapshot_manager_.PrepareDeltas(
@@ skipping 63 matching lines @@
         histogram_flattener_delta_recorder_.GetRecordedDeltaHistogramNames();
     EXPECT_EQ(2U, histograms.size());
     EXPECT_EQ(3, histogram_flattener_delta_recorder_.
                      GetRecordedDeltaHistogramSum("UmaHistogram"));
     EXPECT_EQ(2, histogram_flattener_delta_recorder_.
                      GetRecordedDeltaHistogramSum("UmaStabilityHistogram"));
   }
 }
 
 }  // namespace base