De-duplicate ranges information in persistent memory.

base/metrics/statistics_recorder.cc

Index: base/metrics/statistics_recorder.cc
diff --git a/base/metrics/statistics_recorder.cc b/base/metrics/statistics_recorder.cc
index ba2101bccf50489ab4284801fd483e06f222fabc..f0ca72c100fbee8dbb5a4f23e7d24ed0baab3c1b 100644
--- a/base/metrics/statistics_recorder.cc
+++ b/base/metrics/statistics_recorder.cc
@@ -431,8 +431,20 @@ size_t StatisticsRecorder::GetHistogramCount() {
 
 // static
 void StatisticsRecorder::ForgetHistogramForTesting(base::StringPiece name) {
-  if (histograms_)
-    histograms_->erase(name);
+  if (!histograms_)
+    return;
+
+  HistogramMap::iterator found = histograms_->find(name);
+  if (found == histograms_->end())
+    return;
+
+  HistogramBase* base = found->second;
+  if (base->GetHistogramType() != SPARSE_HISTOGRAM) {

[Alexei Svitkine (slow), 2017/04/04 17:45:09]

Nit: Add a comment about this logic.

[bcwhite, 2017/04/05 13:41:30]

Done.

+    Histogram* histogram = static_cast<Histogram*>(base);
+    histogram->bucket_ranges()->set_persistent_reference(0);
+  }
+
+  histograms_->erase(found);
 }
 
 // static