Persist setup metrics and have Chrome report them during UMA upload.

base/metrics/histogram_snapshot_manager.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.
 
 #ifndef BASE_METRICS_HISTOGRAM_SNAPSHOT_MANAGER_H_
 #define BASE_METRICS_HISTOGRAM_SNAPSHOT_MANAGER_H_
 
 #include <stdint.h>
 
 #include <map>
 #include <string>
+#include <vector>
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/metrics/histogram_base.h"
 
 namespace base {
 
 class HistogramSamples;
 class HistogramFlattener;
 
@@ skipping 54 matching lines @@
     FinishDeltas();
   }
 
   // When the collection is not so simple as can be done using a single
   // iterator, the steps can be performed separately. Call PerpareDelta()
   // as many times as necessary with a single StartDeltas() before and
   // a single FinishDeltas() after. All passed histograms must live
   // until FinishDeltas() completes. PrepareOnce() works the same
   // but assumes there were no previous logged values and no future deltas
   // will be created (and thus can work on read-only histograms).
+  // Use Prepare*TakingOwnership() if it is desireable to have this class
+  // automatically delete the histogram once it is "finished".
   void StartDeltas();
   void PrepareDelta(HistogramBase* histogram);
+  void PrepareDeltaTakingOwnership(HistogramBase* histogram);
   void PrepareOnce(const HistogramBase* histogram);
+  void PrepareOnceTakingOwnership(const HistogramBase* histogram);
   void FinishDeltas();
 
  private:
   FRIEND_TEST_ALL_PREFIXES(HistogramSnapshotManagerTest, CheckMerge);
 
   // Capture and hold samples from a histogram. This does all the heavy
   // lifting for PrepareDelta() and PrepareOnce().
   void PrepareSamples(const HistogramBase* histogram,
-                      scoped_ptr<HistogramSamples> samples);
+                      scoped_ptr<HistogramSamples> samples,
+                      bool take_ownership);
 
   // Try to detect and fix count inconsistency of logged samples.
   void InspectLoggedSamplesInconsistency(
       const HistogramSamples& new_snapshot,
       HistogramSamples* logged_samples);
 
   // For histograms, track what has been previously seen, indexed
   // by the hash of the histogram name.
   HashInfoMap known_histograms_;
 
+  // Collection of histograms of which ownership has been passed to this
+  // object. They will be deleted by FinishDeltas().
+  std::vector<const HistogramBase*> owned_histograms_;

[grt (UTC plus 2), 2016/02/08 18:09:18]

use std::vector<scoped_ptr<HistogramBase>> here. clearing the vector will
automagically delete all of the histograms.

[bcwhite, 2016/02/09 21:08:45]

Done.  Is this new?  A lot of code uses STL utils to clear pointers.

[grt (UTC plus 2), 2016/02/10 16:01:53]

It is fairly new, yes:
https://groups.google.com/a/chromium.org/d/msg/chromium-dev/PizeR1qUJdk/JQd0a...

+
   // Indicates if deltas are currently being prepared.
   bool preparing_deltas_;
 
   // |histogram_flattener_| handles the logistics of recording the histogram
   // deltas.
   HistogramFlattener* histogram_flattener_;  // Weak.
 
   DISALLOW_COPY_AND_ASSIGN(HistogramSnapshotManager);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_HISTOGRAM_SNAPSHOT_MANAGER_H_