Add support for persistent sparse histograms.

base/metrics/sparse_histogram.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_METRICS_SPARSE_HISTOGRAM_H_
 #define BASE_METRICS_SPARSE_HISTOGRAM_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 33 matching lines @@
 // Likewise Sqlite.Error.* are SPARSE, because most databases generate few or no
 // errors and there are large gaps in the set of possible errors.
 #define UMA_HISTOGRAM_SPARSE_SLOWLY(name, sample) \
     do { \
       base::HistogramBase* histogram = base::SparseHistogram::FactoryGet( \
           name, base::HistogramBase::kUmaTargetedHistogramFlag); \
       histogram->Add(sample); \
     } while (0)
 
 class HistogramSamples;
+class PersistentMemoryAllocator;
 
 class BASE_EXPORT SparseHistogram : public HistogramBase {
  public:
   // If there's one with same name, return the existing one. If not, create a
   // new one.
   static HistogramBase* FactoryGet(const std::string& name, int32_t flags);
 
+  // Create a histogram using data in persistent storage.
+  static scoped_ptr<HistogramBase> PersistentCreate(
+      PersistentMemoryAllocator* allocator,
+      const std::string& name,
+      HistogramSamples::Metadata* meta,
+      HistogramSamples::Metadata* logged_meta);
+
   ~SparseHistogram() override;
 
   // HistogramBase implementation:
   uint64_t name_hash() const override;
   HistogramType GetHistogramType() const override;
   bool HasConstructionArguments(Sample expected_minimum,
                                 Sample expected_maximum,
                                 uint32_t expected_bucket_count) const override;
   void Add(Sample value) override;
   void AddCount(Sample value, int count) override;
   void AddSamples(const HistogramSamples& samples) override;
   bool AddSamplesFromPickle(base::PickleIterator* iter) override;
   scoped_ptr<HistogramSamples> SnapshotSamples() const override;
   scoped_ptr<HistogramSamples> SnapshotDelta() override;
   void WriteHTMLGraph(std::string* output) const override;
   void WriteAscii(std::string* output) const override;
 
  protected:
   // HistogramBase implementation:
   bool SerializeInfoImpl(base::Pickle* pickle) const override;
 
  private:
   // Clients should always use FactoryGet to create SparseHistogram.
   explicit SparseHistogram(const std::string& name);
 
+  SparseHistogram(PersistentMemoryAllocator* allocator,
+                  const std::string& name,
+                  HistogramSamples::Metadata* meta,
+                  HistogramSamples::Metadata* logged_meta);
+
   friend BASE_EXPORT HistogramBase* DeserializeHistogramInfo(
       base::PickleIterator* iter);
   static HistogramBase* DeserializeInfoImpl(base::PickleIterator* iter);
 
   void GetParameters(DictionaryValue* params) const override;
   void GetCountAndBucketData(Count* count,
                              int64_t* sum,
                              ListValue* buckets) const override;
 
   // Helpers for emitting Ascii graphic.  Each method appends data to output.
   void WriteAsciiImpl(bool graph_it,
                       const std::string& newline,
                       std::string* output) const;
 
   // Write a common header message describing this histogram.
   void WriteAsciiHeader(const Count total_count,
                         std::string* output) const;
 
   // For constuctor calling.
   friend class SparseHistogramTest;
 
   // Protects access to |samples_|.
   mutable base::Lock lock_;
 
-  SampleMap samples_;
-  SampleMap logged_samples_;
+  scoped_ptr<HistogramSamples> samples_;
+  scoped_ptr<HistogramSamples> logged_samples_;
 
   DISALLOW_COPY_AND_ASSIGN(SparseHistogram);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_SPARSE_HISTOGRAM_H_