Reorganize histograms for persistence.

base/metrics/sample_vector.h

Index: base/metrics/sample_vector.h
diff --git a/base/metrics/sample_vector.h b/base/metrics/sample_vector.h
index 8cb2ab9e0a6db364937c5ea5de7171d741715513..00b476f532cb63312f6dcb39b9492b97049303e4 100644
--- a/base/metrics/sample_vector.h
+++ b/base/metrics/sample_vector.h
@@ -23,6 +23,12 @@ class BucketRanges;
 class BASE_EXPORT SampleVector : public HistogramSamples {
  public:
   explicit SampleVector(const BucketRanges* bucket_ranges);
+  SampleVector(uint64 id, const BucketRanges* bucket_ranges);
+  SampleVector(uint64 id,
+               HistogramBase::AtomicCount* counts,
+               size_t counts_size,
+               Metadata* meta,
+               const BucketRanges* bucket_ranges);
   ~SampleVector() override;
 
   // HistogramSamples implementation:
@@ -45,7 +51,14 @@ class BASE_EXPORT SampleVector : public HistogramSamples {
  private:
   FRIEND_TEST_ALL_PREFIXES(HistogramTest, CorruptSampleCounts);
 
-  std::vector<HistogramBase::AtomicCount> counts_;
+  // In the case where this class manages the memory, here it is.
+  std::vector<HistogramBase::AtomicCount> local_counts_;
+
+  // These are raw pointers rather than objects for flexibility. The actual
+  // memory is either managed by local_counts_ above or by an external object
+  // and passed in directly.
+  HistogramBase::AtomicCount* counts_;
+  size_t counts_size_;
 
   // Shares the same BucketRanges with Histogram object.
   const BucketRanges* const bucket_ranges_;
@@ -57,6 +70,9 @@ class BASE_EXPORT SampleVectorIterator : public SampleCountIterator {
  public:
   SampleVectorIterator(const std::vector<HistogramBase::AtomicCount>* counts,
                        const BucketRanges* bucket_ranges);
+  SampleVectorIterator(const HistogramBase::AtomicCount* counts,
+                       size_t counts_size,
+                       const BucketRanges* bucket_ranges);
   ~SampleVectorIterator() override;
 
   // SampleCountIterator implementation:
@@ -72,7 +88,8 @@ class BASE_EXPORT SampleVectorIterator : public SampleCountIterator {
  private:
   void SkipEmptyBuckets();
 
-  const std::vector<HistogramBase::AtomicCount>* counts_;
+  const HistogramBase::AtomicCount* counts_;

[Alexei Svitkine (slow), 2015/12/01 16:32:14]

Can this be "const HistogramBase::AtomicCount* const" counts ? i.e. the pointer
doesn't change after ctor call. Same for bucket_ranges.

+  size_t counts_size_;

[Alexei Svitkine (slow), 2015/12/01 16:32:14]

Make this const

   const BucketRanges* bucket_ranges_;
 
   size_t index_;