Merge multiple histogram snapshots into single one for reporting.

base/metrics/histogram.h

Index: base/metrics/histogram.h
diff --git a/base/metrics/histogram.h b/base/metrics/histogram.h
index 4e722aa20d91da7a1a0cd318150ee1a40c266830..6a54b148bdc8034ab8041f7b6e392b6d01ce8f67 100644
--- a/base/metrics/histogram.h
+++ b/base/metrics/histogram.h
@@ -145,6 +145,7 @@ class BASE_EXPORT Histogram : public HistogramBase {
                                       Sample maximum,
                                       const BucketRanges* ranges,
                                       HistogramBase::AtomicCount* counts,
+                                      HistogramBase::AtomicCount* logged,
                                       uint32_t counts_size,
                                       HistogramSamples::Metadata* meta);
 
@@ -197,6 +198,7 @@ class BASE_EXPORT Histogram : public HistogramBase {
   void Add(Sample value) override;
   void AddCount(Sample value, int count) override;
   scoped_ptr<HistogramSamples> SnapshotSamples() const override;
+  scoped_ptr<HistogramSamples> SnapshotDelta() override;
   void AddSamples(const HistogramSamples& samples) override;
   bool AddSamplesFromPickle(base::PickleIterator* iter) override;
   void WriteHTMLGraph(std::string* output) const override;
@@ -228,6 +230,7 @@ class BASE_EXPORT Histogram : public HistogramBase {
             Sample maximum,
             const BucketRanges* ranges,
             HistogramBase::AtomicCount* counts,
+            HistogramBase::AtomicCount* logged,

[Alexei Svitkine (slow), 2016/02/09 19:46:51]

Nit: logged_counts

Change everywhere.

[bcwhite, 2016/02/11 16:42:38]

Done.

             uint32_t counts_size,
             HistogramSamples::Metadata* meta);
 
@@ -303,6 +306,9 @@ class BASE_EXPORT Histogram : public HistogramBase {
   // sample.
   scoped_ptr<SampleVector> samples_;
 
+  // Also keep a previous uploaded state for calculating deltas.
+  scoped_ptr<HistogramSamples> logged_;
+
   DISALLOW_COPY_AND_ASSIGN(Histogram);
 };
 
@@ -347,6 +353,7 @@ class BASE_EXPORT LinearHistogram : public Histogram {
                                       Sample maximum,
                                       const BucketRanges* ranges,
                                       HistogramBase::AtomicCount* counts,
+                                      HistogramBase::AtomicCount* logged,
                                       uint32_t counts_size,
                                       HistogramSamples::Metadata* meta);
 
@@ -388,6 +395,7 @@ class BASE_EXPORT LinearHistogram : public Histogram {
                   Sample maximum,
                   const BucketRanges* ranges,
                   HistogramBase::AtomicCount* counts,
+                  HistogramBase::AtomicCount* logged,
                   uint32_t counts_size,
                   HistogramSamples::Metadata* meta);
 
@@ -431,6 +439,7 @@ class BASE_EXPORT BooleanHistogram : public LinearHistogram {
   static HistogramBase* PersistentGet(const std::string& name,
                                       const BucketRanges* ranges,
                                       HistogramBase::AtomicCount* counts,
+                                      HistogramBase::AtomicCount* logged,
                                       HistogramSamples::Metadata* meta);
 
   HistogramType GetHistogramType() const override;
@@ -443,6 +452,7 @@ class BASE_EXPORT BooleanHistogram : public LinearHistogram {
   BooleanHistogram(const std::string& name,
                    const BucketRanges* ranges,
                    HistogramBase::AtomicCount* counts,
+                   HistogramBase::AtomicCount* logged,
                    HistogramSamples::Metadata* meta);
 
   friend BASE_EXPORT HistogramBase* DeserializeHistogramInfo(
@@ -476,6 +486,7 @@ class BASE_EXPORT CustomHistogram : public Histogram {
   static HistogramBase* PersistentGet(const std::string& name,
                                       const BucketRanges* ranges,
                                       HistogramBase::AtomicCount* counts,
+                                      HistogramBase::AtomicCount* logged,
                                       uint32_t counts_size,
                                       HistogramSamples::Metadata* meta);
 
@@ -499,6 +510,7 @@ class BASE_EXPORT CustomHistogram : public Histogram {
   CustomHistogram(const std::string& name,
                   const BucketRanges* ranges,
                   HistogramBase::AtomicCount* counts,
+                  HistogramBase::AtomicCount* logged,
                   uint32_t counts_size,
                   HistogramSamples::Metadata* meta);