Fix StatisticsRecorder to handle re-entry during tests.

base/metrics/statistics_recorder.h

 // 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.
 
 // StatisticsRecorder holds all Histograms and BucketRanges that are used by
 // Histograms in the system. It provides a general place for
 // Histograms/BucketRanges to register, and supports a global API for accessing
 // (i.e., dumping, or graphing) the data.
 
 #ifndef BASE_METRICS_STATISTICS_RECORDER_H_
@@ skipping 112 matching lines @@
 
   // ClearCallback clears any callback set on the histogram referred to by
   // |histogram_name|. This method is thread safe.
   static void ClearCallback(const std::string& histogram_name);
 
   // FindCallback retrieves the callback for the histogram referred to by
   // |histogram_name|, or a null callback if no callback exists for this
   // histogram. This method is thread safe.
   static OnSampleCallback FindCallback(const std::string& histogram_name);
 
-  // Clears all of the known histograms and resets static variables to a
-  // state that allows a new initialization.
-  static void ResetForTesting();
-
   // Removes a histogram from the internal set of known ones. This can be
   // necessary during testing persistent histograms where the underlying
   // memory is being released.
   static void ForgetHistogramForTesting(base::StringPiece name);
 
  private:
   // We keep a map of callbacks to histograms, so that as histograms are
   // created, we can set the callback properly.
   typedef std::map<std::string, OnSampleCallback> CallbackMap;
 
@@ skipping 12 matching lines @@
   friend class StatisticsRecorderTest;
   FRIEND_TEST_ALL_PREFIXES(HistogramDeltaSerializationTest,
                            DeserializeHistogramAndAddSamples);
 
   // The constructor just initializes static members. Usually client code should
   // use Initialize to do this. But in test code, you can friend this class and
   // call destructor/constructor to get a clean StatisticsRecorder.
   StatisticsRecorder();
   ~StatisticsRecorder();
 
+  // These are copies of everything that existed when the (test) Statistics-
+  // Recorder was created. The global ones have to be moved aside to create a
+  // clean environment.
+  scoped_ptr<HistogramMap> existing_histograms_;
+  scoped_ptr<CallbackMap> existing_callbacks_;
+  scoped_ptr<RangesMap> existing_ranges_;

[Alexei Svitkine (slow), 2016/03/08 20:04:12]

Can this be done in a test-only subclass?

[bcwhite, 2016/03/08 20:23:27]

Potentially.  It'll require turning private members into protected ones.

It's already basically a test-only class except for the one global instance. 
We'll waste 3 pointers worth of memory on that instance.  Still think it's worth
it?

+
   static void Reset();
   static void DumpHistogramsToVlog(void* instance);
 
   static HistogramMap* histograms_;
   static CallbackMap* callbacks_;
   static RangesMap* ranges_;
 
   // Lock protects access to above maps.
   static base::Lock* lock_;
 
   DISALLOW_COPY_AND_ASSIGN(StatisticsRecorder);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_STATISTICS_RECORDER_H_