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..a12c0f5536f22e367848310cbbee2d8e832b3297 100644
--- a/base/metrics/sample_vector.h
+++ b/base/metrics/sample_vector.h
@@ -22,7 +22,12 @@ 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 +50,14 @@ 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 +69,9 @@ 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 +87,8 @@ class BASE_EXPORT SampleVectorIterator : public SampleCountIterator {
  private:
   void SkipEmptyBuckets();
 
-  const std::vector<HistogramBase::AtomicCount>* counts_;
+  const HistogramBase::AtomicCount* counts_;
+  size_t counts_size_;
   const BucketRanges* bucket_ranges_;
 
   size_t index_;