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

base/metrics/histogram_snapshot_manager.h

Index: base/metrics/histogram_snapshot_manager.h
diff --git a/base/metrics/histogram_snapshot_manager.h b/base/metrics/histogram_snapshot_manager.h
index 97bd693966fd6b1ed8ef2c84bcaaafee9eb8a0bc..c991fa6e64d597b2b7db8849bd5e13f97f142060 100644
--- a/base/metrics/histogram_snapshot_manager.h
+++ b/base/metrics/histogram_snapshot_manager.h
@@ -9,6 +9,7 @@
 
 #include <map>
 #include <string>
+#include <vector>
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
@@ -83,9 +84,13 @@ class BASE_EXPORT HistogramSnapshotManager {
   // 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);

[grt (UTC plus 2), 2016/02/04 15:36:42]

take a scoped_ptr rather than a raw ptr so that the ownership transfer is
explicit

[bcwhite, 2016/02/04 21:51:13]

These call through to the private PrepareSamples which *doesn't* (and can't)
take a scoped_ptr.  I'll have to release the scoped_ptr in the implementation to
pass a raw pointer to that method.  Okay?

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

SGTM.

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

Done.

   void PrepareOnce(const HistogramBase* histogram);
+  void PrepareOnceTakingOwnership(const HistogramBase* histogram);
   void FinishDeltas();
 
  private:
@@ -94,7 +99,8 @@ class BASE_EXPORT HistogramSnapshotManager {
   // 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(
@@ -105,6 +111,10 @@ class BASE_EXPORT HistogramSnapshotManager {
   // 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_;
+
   // Indicates if deltas are currently being prepared.
   bool preparing_deltas_;