Add SampleMap and use it in SparseHistogram

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 05a68b53540a1f5daf23c62c8ac6b6faa94e4006..bc1913f5ea586709a9e63a54109b4c821c3c9fdc 100644
--- a/base/metrics/sparse_histogram.cc
+++ b/base/metrics/sparse_histogram.cc
@@ -5,14 +5,18 @@
 #include "base/metrics/sparse_histogram.h"
 
 #include "base/metrics/statistics_recorder.h"
+#include "base/synchronization/lock.h"
 
+using std::map;
 using std::string;
 
 namespace base {
 
+typedef HistogramBase::Count Count;
+typedef HistogramBase::Sample Sample;
+
 // static
-HistogramBase* SparseHistogram::FactoryGet(const string& name,
-                                           int32 flags) {
+HistogramBase* SparseHistogram::FactoryGet(const string& name, int32 flags) {
   // TODO(kaiwang): Register and get SparseHistogram with StatisticsRecorder.
   HistogramBase* histogram = new SparseHistogram(name);
   histogram->SetFlags(flags);
@@ -23,12 +27,21 @@ SparseHistogram::~SparseHistogram() {}
 
 void SparseHistogram::Add(Sample value) {
   base::AutoLock auto_lock(lock_);
-  samples_[value]++;
+  sample_counts_[value]++;
+  redundant_count_ += 1;
 }
 
-void SparseHistogram::SnapshotSample(std::map<Sample, Count>* samples) const {
+scoped_ptr<SampleMap> SparseHistogram::SnapshotSamples() const {
+  scoped_ptr<SampleMap> snapshot(new SampleMap());
+
   base::AutoLock auto_lock(lock_);
-  *samples = samples_;
+  for(map<Sample, Count>::const_iterator it = sample_counts_.begin();
+      it != sample_counts_.end();
+      ++it) {
+    snapshot->Accumulate(it->first, it->second);
+  }
+  snapshot->ResetRedundantCount(redundant_count_);
+  return snapshot.Pass();
 }
 
 void SparseHistogram::WriteHTMLGraph(string* output) const {
@@ -40,6 +53,7 @@ void SparseHistogram::WriteAscii(string* output) const {
 }
 
 SparseHistogram::SparseHistogram(const string& name)
-    : HistogramBase(name) {}
+    : HistogramBase(name),
+      redundant_count_(0) {}
 
 }  // namespace base