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 e03213fc72104774fc9568601e6f537952693847..0c299301be048f33502de5fc74fc8a95495427df 100644
--- a/base/metrics/histogram_snapshot_manager.cc
+++ b/base/metrics/histogram_snapshot_manager.cc
@@ -27,8 +27,9 @@ 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 &
@@ -38,19 +39,33 @@ 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::PrepareAbsolute(const HistogramBase* histogram) {
-  PrepareSamples(histogram, histogram->SnapshotSamples());
+  PrepareSamples(histogram, histogram->SnapshotSamples(), false);
+}
+
+void HistogramSnapshotManager::PrepareAbsoluteTakingOwnership(
+    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() {
   DCHECK(preparing_deltas_);
 
   // Iterate over all known histograms to see what should be recorded.
-  for (auto& iter : known_histograms_) {
-    SampleInfo* sample_info = &iter.second;
+  for (auto& hash_and_info : known_histograms_) {
+    SampleInfo* sample_info = &hash_and_info.second;
 
     // First, record any histograms in which corruption was detected.
     if (sample_info->inconsistencies & HistogramBase::NEW_INCONSISTENCY_FOUND) {
@@ -77,22 +92,33 @@ void HistogramSnapshotManager::FinishDeltas() {
     sample_info->histogram = nullptr;
   }
 
+  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);

[Alexei Svitkine (slow), 2016/02/19 18:16:40]

I don't think we need this extra complexity. Storing the histogram until
Finished unconditionally should be fine in all cases.

If so, you can simplify the code by reverting changes to this function and just
have the *TakeOwnership() functions directly add to |owned_histograms_| after
calling this.

[bcwhite, 2016/02/19 19:50:14]

Done.

   } 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