Merge multiple histogram snapshots into single one for reporting.

components/metrics/metrics_service.cc

Index: components/metrics/metrics_service.cc
diff --git a/components/metrics/metrics_service.cc b/components/metrics/metrics_service.cc
index e868ea7c9bb1cc087644257b65c44e3edcf9e346..ebbf4275bed5dd764109315a5a0cfbeb709abce6 100644
--- a/components/metrics/metrics_service.cc
+++ b/components/metrics/metrics_service.cc
@@ -252,10 +252,12 @@ SyntheticTrialGroup::~SyntheticTrialGroup() {
 }
 
 MetricsService::PersistentHistogramIterator::PersistentHistogramIterator(
+    HistogramSet* found_histograms,
     AllocatorSet& allocators,
     AllocatorSet::iterator pos)
     : allocators_(allocators),
-      allocator_iter_(pos) {
+      allocator_iter_(pos),
+      found_histograms_(found_histograms) {
   if (pos != allocators_.end()) {
     (*allocator_iter_)->CreateIterator(&histogram_iter_);
     // Have to call ++ to advance iterator to the first persistent histogram.
@@ -267,10 +269,12 @@ MetricsService::PersistentHistogramIterator&
 MetricsService::PersistentHistogramIterator::operator++() {
   if (allocator_iter_ != allocators_.end()) {
     for (;;) {
-      base::HistogramBase* h = base::HistogramBase::GetNextPersistentHistogram(
+      current_histogram_ = base::HistogramBase::GetNextPersistentHistogram(
           *allocator_iter_, &histogram_iter_);
-      if (h) {
-        current_histogram_ = new HistogramPointer(h);
+      if (current_histogram_) {
+        DCHECK(found_histograms_->find(current_histogram_) ==
+               found_histograms_->end());
+        found_histograms_->insert(current_histogram_);
         break;
       }
       allocator_iter_++;
@@ -1158,9 +1162,11 @@ void MetricsService::RecordCurrentHistograms() {
   histogram_snapshot_manager_.PrepareDeltas(
       base::StatisticsRecorder::begin(true), base::StatisticsRecorder::end(),
       base::Histogram::kNoFlags, base::Histogram::kUmaTargetedHistogramFlag);
+  HistogramSet persistent_histograms;
   histogram_snapshot_manager_.PrepareDeltas(
-      persistent_begin(), persistent_end(),
+      persistent_begin(&persistent_histograms), persistent_end(),
       base::Histogram::kNoFlags, base::Histogram::kUmaTargetedHistogramFlag);
+  STLDeleteElements(&persistent_histograms);
 }
 
 void MetricsService::RecordCurrentStabilityHistograms() {
@@ -1205,12 +1211,13 @@ void MetricsService::SkipAndDiscardUpload() {
   log_upload_in_progress_ = false;
 }
 
-MetricsService::PersistentHistogramIterator MetricsService::persistent_begin() {
-  return PersistentHistogramIterator(allocators_, allocators_.begin());
+MetricsService::PersistentHistogramIterator MetricsService::persistent_begin(
+    HistogramSet* found) {
+  return PersistentHistogramIterator(found, allocators_, allocators_.begin());
 }
 
 MetricsService::PersistentHistogramIterator MetricsService::persistent_end() {
-  return PersistentHistogramIterator(allocators_, allocators_.end());
+  return PersistentHistogramIterator(nullptr, allocators_, allocators_.end());
 }
 
 }  // namespace metrics