Add support for persistent sparse histograms.

base/metrics/sample_map.cc

Index: base/metrics/sample_map.cc
diff --git a/base/metrics/sample_map.cc b/base/metrics/sample_map.cc
index e276b91643b6a4fa567b2e4f84eb09b94a92a38c..90f47d3d70abc52e2d35bd605d3ef99f6ee83a1f 100644
--- a/base/metrics/sample_map.cc
+++ b/base/metrics/sample_map.cc
@@ -5,12 +5,74 @@
 #include "base/metrics/sample_map.h"
 
 #include "base/logging.h"
+#include "base/stl_util.h"
 
 namespace base {
 
 typedef HistogramBase::Count Count;
 typedef HistogramBase::Sample Sample;
 
+namespace {
+
+// An iterator for going through a SampleMap.
+class SampleMapIterator : public SampleCountIterator {
+ public:
+  typedef std::map<HistogramBase::Sample, HistogramBase::Count>
+      SampleToCountMap;
+
+  explicit SampleMapIterator(const SampleToCountMap& sample_counts);
+  ~SampleMapIterator() override;
+
+  // SampleCountIterator:
+  bool Done() const override;
+  void Next() override;
+  void Get(HistogramBase::Sample* min,
+           HistogramBase::Sample* max,
+           HistogramBase::Count* count) const override;
+
+ private:
+  void SkipEmptyBuckets();
+
+  SampleToCountMap::const_iterator iter_;
+  const SampleToCountMap::const_iterator end_;
+};
+
+SampleMapIterator::SampleMapIterator(const SampleToCountMap& sample_counts)
+    : iter_(sample_counts.begin()),
+      end_(sample_counts.end()) {
+  SkipEmptyBuckets();
+}
+
+SampleMapIterator::~SampleMapIterator() {}
+
+bool SampleMapIterator::Done() const {
+  return iter_ == end_;
+}
+
+void SampleMapIterator::Next() {
+  DCHECK(!Done());
+  ++iter_;
+  SkipEmptyBuckets();
+}
+
+void SampleMapIterator::Get(Sample* min, Sample* max, Count* count) const {
+  DCHECK(!Done());
+  if (min)
+    *min = iter_->first;
+  if (max)
+    *max = iter_->first + 1;
+  if (count)
+    *count = iter_->second;
+}
+
+void SampleMapIterator::SkipEmptyBuckets() {
+  while (!Done() && iter_->second == 0) {
+    ++iter_;
+  }
+}
+
+}  // namespace
+
 SampleMap::SampleMap() : SampleMap(0) {}
 
 SampleMap::SampleMap(uint64_t id) : HistogramSamples(id) {}
@@ -32,18 +94,16 @@ Count SampleMap::GetCount(Sample value) const {
 
 Count SampleMap::TotalCount() const {
   Count count = 0;
-  for (const auto& entry : sample_counts_) {
+  for (const auto& entry : sample_counts_)
     count += entry.second;
-  }
   return count;
 }
 
 scoped_ptr<SampleCountIterator> SampleMap::Iterator() const {
-  return scoped_ptr<SampleCountIterator>(new SampleMapIterator(sample_counts_));
+  return make_scoped_ptr(new SampleMapIterator(sample_counts_));
 }
 
-bool SampleMap::AddSubtractImpl(SampleCountIterator* iter,
-                                HistogramSamples::Operator op) {
+bool SampleMap::AddSubtractImpl(SampleCountIterator* iter, Operator op) {
   Sample min;
   Sample max;
   Count count;
@@ -57,38 +117,4 @@ bool SampleMap::AddSubtractImpl(SampleCountIterator* iter,
   return true;
 }
 
-SampleMapIterator::SampleMapIterator(const SampleToCountMap& sample_counts)
-    : iter_(sample_counts.begin()),
-      end_(sample_counts.end()) {
-  SkipEmptyBuckets();
-}
-
-SampleMapIterator::~SampleMapIterator() {}
-
-bool SampleMapIterator::Done() const {
-  return iter_ == end_;
-}
-
-void SampleMapIterator::Next() {
-  DCHECK(!Done());
-  ++iter_;
-  SkipEmptyBuckets();
-}
-
-void SampleMapIterator::Get(Sample* min, Sample* max, Count* count) const {
-  DCHECK(!Done());
-  if (min != NULL)
-    *min = iter_->first;
-  if (max != NULL)
-    *max = iter_->first + 1;
-  if (count != NULL)
-    *count = iter_->second;
-}
-
-void SampleMapIterator::SkipEmptyBuckets() {
-  while (!Done() && iter_->second == 0) {
-    ++iter_;
-  }
-}
-
 }  // namespace base