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

base/metrics/histogram_snapshot_manager.cc

Index: base/metrics/histogram_snapshot_manager.cc
diff --git a/base/metrics/histogram_snapshot_manager.cc b/base/metrics/histogram_snapshot_manager.cc
index 4783462e7535ea841b9899630529a086603759db..41e5bbf46efbb5050391cbf1edea3d262d6fd4c4 100644
--- a/base/metrics/histogram_snapshot_manager.cc
+++ b/base/metrics/histogram_snapshot_manager.cc
@@ -11,8 +11,6 @@
 #include "base/stl_util.h"
 
 namespace {
-// A flag to indicate that a new inconsistency has been added to the set.
-// It is used to know if the value needs to be sent upstream and cleared after.
 const int kNewInconsistency = (int)0x80000000;

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

nit: replace c-style cast with a C++ cast

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

Done.

 }  // namespace
 
@@ -33,8 +31,9 @@ void HistogramSnapshotManager::StartDeltas() {
   DCHECK(!preparing_deltas_);
   preparing_deltas_ = true;
 
+  DCHECK(owned_histograms_.empty());
+
 #ifdef DEBUG
-  for (const auto& iter : known_histograms) {
     CHECK(!iter->second.histogram);
     CHECK(!iter->second.accumulated_samples);
     CHECK(!(iter->second.inconsistencies & kNewInconsistency));
@@ -43,11 +42,25 @@ void HistogramSnapshotManager::StartDeltas() {
 }
 
 void HistogramSnapshotManager::PrepareDelta(HistogramBase* histogram) {
-  PrepareSamples(histogram, histogram->SnapshotDelta());
+  PrepareSamples(histogram, histogram->SnapshotDelta(), false);
+}
+
+void HistogramSnapshotManager::PrepareDeltaTakingOwnership(
+    scoped_ptr<HistogramBase> histogram) {
+  // Snapshot must be done before releasing the pointer.
+  scoped_ptr<HistogramSamples> samples = histogram->SnapshotDelta();
+  PrepareSamples(histogram.release(), std::move(samples), true);
 }
 
 void HistogramSnapshotManager::PrepareOnce(const HistogramBase* histogram) {
-  PrepareSamples(histogram, histogram->SnapshotSamples());
+  PrepareSamples(histogram, histogram->SnapshotSamples(), false);
+}
+
+void HistogramSnapshotManager::PrepareOnceTakingOwnership(
+    scoped_ptr<const HistogramBase> histogram) {
+  // Snapshot must be done before releasing the pointer.
+  scoped_ptr<HistogramSamples> samples = histogram->SnapshotSamples();
+  PrepareSamples(histogram.release(), std::move(samples), true);
 }
 
 void HistogramSnapshotManager::FinishDeltas() {
@@ -82,22 +95,33 @@ void HistogramSnapshotManager::FinishDeltas() {
     sample_info->histogram = nullptr;

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

just curious: should |inconsistencies| also be cleared since the underlying
HistogramBase object is destroyed on line 98?

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

It needs to remain to prevent multiple reports of the inconsistency.  The next
time a snapshot is created, the inconsistency will still be present but we don't
want to continuously report such to the server.

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

groovy, thanks

   }
 
+  owned_histograms_.clear();
   preparing_deltas_ = false;
 }
 
 void HistogramSnapshotManager::PrepareSamples(
     const HistogramBase* histogram,
-    scoped_ptr<HistogramSamples> samples) {
+    scoped_ptr<HistogramSamples> samples,
+    bool take_ownership) {
   DCHECK(histogram_flattener_);
+  scoped_ptr<const HistogramBase> owned_histogram;
 
   // Get information known about this histogram.
   SampleInfo* sample_info = &known_histograms_[histogram->name_hash()];
   if (sample_info->histogram) {
     DCHECK_EQ(sample_info->histogram->histogram_name(),
               histogram->histogram_name()) << "hash collision";
+    // Passed histogram won't be needed past end of this method so store
+    // it in a scoped_ptr that will release it when returning.
+    if (take_ownership)
+      owned_histogram.reset(histogram);
   } else {
     // First time this histogram has been seen; datafill.
     sample_info->histogram = histogram;
+    // The histogram data will be needed up until "finished" so store
+    // in member vector for releasing when that is done.
+    if (take_ownership)
+      owned_histograms_.push_back(make_scoped_ptr(histogram));
   }
 
   // Crash if we detect that our histograms have been overwritten.  This may be