Reorganize histograms for persistence.

base/metrics/sparse_histogram.cc

Index: base/metrics/sparse_histogram.cc
diff --git a/base/metrics/sparse_histogram.cc b/base/metrics/sparse_histogram.cc
index 7955c572811f2c685535f52cdb81f7c94b8955e2..21697fb9a1bcf8e13e75be75b68fc4f45ceb6c41 100644
--- a/base/metrics/sparse_histogram.cc
+++ b/base/metrics/sparse_histogram.cc
@@ -6,6 +6,7 @@
 
 #include <utility>
 
+#include "base/metrics/metrics_hashes.h"
 #include "base/metrics/sample_map.h"
 #include "base/metrics/statistics_recorder.h"
 #include "base/pickle.h"
@@ -35,6 +36,10 @@ HistogramBase* SparseHistogram::FactoryGet(const std::string& name,
 
 SparseHistogram::~SparseHistogram() {}
 
+uint64_t SparseHistogram::name_hash() const {
+  return samples_.id();
+}
+
 HistogramType SparseHistogram::GetHistogramType() const {
   return SPARSE_HISTOGRAM;
 }
@@ -65,7 +70,8 @@ void SparseHistogram::AddCount(Sample value, int count) {
 }
 
 scoped_ptr<HistogramSamples> SparseHistogram::SnapshotSamples() const {
-  scoped_ptr<SampleMap> snapshot(new SampleMap());
+  scoped_ptr<SampleMap> snapshot(
+      new SampleMap(HashMetricName(histogram_name())));

[Alexei Svitkine (slow), 2015/12/09 23:03:40]

Pass in name_hash() instead.

[bcwhite, 2015/12/10 14:51:33]

Done.

 
   base::AutoLock auto_lock(lock_);
   snapshot->Add(samples_);
@@ -97,7 +103,8 @@ bool SparseHistogram::SerializeInfoImpl(Pickle* pickle) const {
 }
 
 SparseHistogram::SparseHistogram(const std::string& name)
-    : HistogramBase(name) {}
+    : HistogramBase(name),
+      samples_(HashMetricName(name)) {}
 
 HistogramBase* SparseHistogram::DeserializeInfoImpl(PickleIterator* iter) {
   std::string histogram_name;