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

base/metrics/histogram_snapshot_manager_unittest.cc

Index: base/metrics/histogram_snapshot_manager_unittest.cc
diff --git a/base/metrics/histogram_snapshot_manager_unittest.cc b/base/metrics/histogram_snapshot_manager_unittest.cc
index 8ec03daa8d97c9579f97dc949c18bfe59c02eb2f..6d53c86ac58319d83b74d7f7d6d53794da1f14ac 100644
--- a/base/metrics/histogram_snapshot_manager_unittest.cc
+++ b/base/metrics/histogram_snapshot_manager_unittest.cc
@@ -68,11 +68,12 @@ class HistogramFlattenerDeltaRecorder : public HistogramFlattener {
 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_;
 };