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

base/metrics/statistics_recorder.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 <memory>
 
 #include "base/at_exit.h"
 #include "base/debug/leak_annotations.h"
 #include "base/json/string_escape.h"
 #include "base/logging.h"
+#include "base/memory/ptr_util.h"
 #include "base/metrics/histogram.h"
 #include "base/metrics/metrics_hashes.h"
 #include "base/metrics/persistent_histogram_allocator.h"
 #include "base/stl_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/synchronization/lock.h"
 #include "base/values.h"
 
 namespace {
 
@@ skipping 391 matching lines @@
   return histograms_->size();
 }
 
 // static
 void StatisticsRecorder::ForgetHistogramForTesting(base::StringPiece name) {
   if (histograms_)
     histograms_->erase(name);
 }
 
 // static
+std::unique_ptr<StatisticsRecorder>
+StatisticsRecorder::CreateTemporaryForTesting() {
+  return WrapUnique(new StatisticsRecorder());
+}
+
+// static
 void StatisticsRecorder::UninitializeForTesting() {
   // Stop now if it's never been initialized.
   if (lock_ == NULL || histograms_ == NULL)
     return;
 
   // Get the global instance and destruct it. It's held in static memory so
   // can't "delete" it; call the destructor explicitly.
   DCHECK(g_statistics_recorder_.private_instance_);
   g_statistics_recorder_.Get().~StatisticsRecorder();
 
@@ skipping 79 matching lines @@
 // static
 StatisticsRecorder::HistogramMap* StatisticsRecorder::histograms_ = NULL;
 // static
 StatisticsRecorder::CallbackMap* StatisticsRecorder::callbacks_ = NULL;
 // static
 StatisticsRecorder::RangesMap* StatisticsRecorder::ranges_ = NULL;
 // static
 base::Lock* StatisticsRecorder::lock_ = NULL;
 
 }  // namespace base