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..db76a8a9e00911fd3c4c8008530e775d29e2d231 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 +70,7 @@ 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(name_hash()));
 
   base::AutoLock auto_lock(lock_);
   snapshot->Add(samples_);
@@ -97,7 +102,8 @@ 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;