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 32 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(scoped_ptr<HistogramBase> histogram);
   void PrepareOnce(const HistogramBase* histogram);
+  void PrepareOnceTakingOwnership(scoped_ptr<const HistogramBase> histogram);
   void FinishDeltas();
 
  private:
   FRIEND_TEST_ALL_PREFIXES(HistogramSnapshotManagerTest, CheckMerge);
 
   // During a snapshot, samples are acquired and aggregated. This structure
   // contains all the information collected for a given histogram. Once a
   // snapshot operation is finished, it is generally emptied except for
   // information that must persist from one report to the next, such as
   // the "inconsistencies".
   struct SampleInfo {
     SampleInfo() : histogram(nullptr),

[grt (UTC plus 2), 2016/02/15 15:42:39]

move the initializers down to the members themselves as per "Non-Static Class
Member Initializers" in http://chromium-cpp.appspot.com/#core-whitelist

[bcwhite, 2016/02/15 19:22:10]

Cool.  I didn't even know about that.

                    accumulated_samples(nullptr),
                    inconsistencies(0) {}
 
     // A histogram associated with this sample; it may be one of many if
     // several have been aggregated into the same "accumulated" sample set.
     // Ownership of the histogram remains elsewhere and this pointer is
     // cleared by FinishDeltas().
     const HistogramBase* histogram;
 
     // The current snapshot-delta values being accumulated.
     // TODO(bcwhite): Change this to a scoped_ptr once all build architectures
     // support such as the value of a std::map.
     HistogramSamples* accumulated_samples;
 
     // The set of inconsistencies (flags) already seen for the histogram.
     // See HistogramBase::Inconsistency for values.
     int inconsistencies;

[grt (UTC plus 2), 2016/02/15 15:42:39]

use unsigned types for bitfields since some shifts are undefined for signed
types. even if you're not doing any shifting, it's a simple rule of thumb to
follow globally. uint32_t is the same size as |int|, so that seems like a good
choice here.

[bcwhite, 2016/02/15 19:22:10]

Okay but I'll do it elsewhere, either in the parent CL that defined this or 3rd
CL since it also goes into existing code.

[grt (UTC plus 2), 2016/02/15 19:53:55]

sgtm

   };
 
   // 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.
   std::map<uint64_t, SampleInfo> known_histograms_;
 
+  // Collection of histograms of which ownership has been passed to this
+  // object. They will be deleted by FinishDeltas().
+  std::vector<scoped_ptr<const HistogramBase>> owned_histograms_;
+
   // 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_