Embed a single sample in histogram metadata.

base/metrics/histogram.h

Index: base/metrics/histogram.h
diff --git a/base/metrics/histogram.h b/base/metrics/histogram.h
index a76dd63226131b873490546965c9f572a1b2ce7c..98c07aa39f8db5020d6c4abdffba33e5847b6e50 100644
--- a/base/metrics/histogram.h
+++ b/base/metrics/histogram.h
@@ -86,11 +86,13 @@ namespace base {
 
 class BooleanHistogram;
 class CustomHistogram;
+class DelayedPersistentAllocation;
 class Histogram;
 class LinearHistogram;
 class Pickle;
 class PickleIterator;
 class SampleVector;
+class SampleVectorBase;
 
 class BASE_EXPORT Histogram : public HistogramBase {
  public:
@@ -142,9 +144,8 @@ class BASE_EXPORT Histogram : public HistogramBase {
       Sample minimum,
       Sample maximum,
       const BucketRanges* ranges,
-      HistogramBase::AtomicCount* counts,
-      HistogramBase::AtomicCount* logged_counts,
-      uint32_t counts_size,
+      const DelayedPersistentAllocation& counts,
+      const DelayedPersistentAllocation& logged_counts,
       HistogramSamples::Metadata* meta,
       HistogramSamples::Metadata* logged_meta);
 
@@ -230,9 +231,8 @@ class BASE_EXPORT Histogram : public HistogramBase {
             Sample minimum,
             Sample maximum,
             const BucketRanges* ranges,
-            HistogramBase::AtomicCount* counts,
-            HistogramBase::AtomicCount* logged_counts,
-            uint32_t counts_size,
+            const DelayedPersistentAllocation& counts,
+            const DelayedPersistentAllocation& logged_counts,
             HistogramSamples::Metadata* meta,
             HistogramSamples::Metadata* logged_meta);
 
@@ -274,10 +274,10 @@ class BASE_EXPORT Histogram : public HistogramBase {
                       std::string* output) const;
 
   // Find out how large (graphically) the largest bucket will appear to be.
-  double GetPeakBucketSize(const SampleVector& samples) const;
+  double GetPeakBucketSize(const SampleVectorBase& samples) const;
 
   // Write a common header message describing this histogram.
-  void WriteAsciiHeader(const SampleVector& samples,
+  void WriteAsciiHeader(const SampleVectorBase& samples,
                         Count sample_count,
                         std::string* output) const;
 
@@ -304,7 +304,7 @@ class BASE_EXPORT Histogram : public HistogramBase {
 
   // Finally, provide the state that changes with the addition of each new
   // sample.
-  std::unique_ptr<SampleVector> samples_;
+  std::unique_ptr<SampleVectorBase> samples_;
 
   // Also keep a previous uploaded state for calculating deltas.
   std::unique_ptr<HistogramSamples> logged_samples_;
@@ -357,9 +357,8 @@ class BASE_EXPORT LinearHistogram : public Histogram {
       Sample minimum,
       Sample maximum,
       const BucketRanges* ranges,
-      HistogramBase::AtomicCount* counts,
-      HistogramBase::AtomicCount* logged_counts,
-      uint32_t counts_size,
+      const DelayedPersistentAllocation& counts,
+      const DelayedPersistentAllocation& logged_counts,
       HistogramSamples::Metadata* meta,
       HistogramSamples::Metadata* logged_meta);
 
@@ -400,9 +399,8 @@ class BASE_EXPORT LinearHistogram : public Histogram {
                   Sample minimum,
                   Sample maximum,
                   const BucketRanges* ranges,
-                  HistogramBase::AtomicCount* counts,
-                  HistogramBase::AtomicCount* logged_counts,
-                  uint32_t counts_size,
+                  const DelayedPersistentAllocation& counts,
+                  const DelayedPersistentAllocation& logged_counts,
                   HistogramSamples::Metadata* meta,
                   HistogramSamples::Metadata* logged_meta);
 
@@ -446,8 +444,8 @@ class BASE_EXPORT BooleanHistogram : public LinearHistogram {
   static std::unique_ptr<HistogramBase> PersistentCreate(
       const std::string& name,
       const BucketRanges* ranges,
-      HistogramBase::AtomicCount* counts,
-      HistogramBase::AtomicCount* logged_counts,
+      const DelayedPersistentAllocation& counts,
+      const DelayedPersistentAllocation& logged_counts,
       HistogramSamples::Metadata* meta,
       HistogramSamples::Metadata* logged_meta);
 
@@ -460,8 +458,8 @@ class BASE_EXPORT BooleanHistogram : public LinearHistogram {
   BooleanHistogram(const std::string& name, const BucketRanges* ranges);
   BooleanHistogram(const std::string& name,
                    const BucketRanges* ranges,
-                   HistogramBase::AtomicCount* counts,
-                   HistogramBase::AtomicCount* logged_counts,
+                   const DelayedPersistentAllocation& counts,
+                   const DelayedPersistentAllocation& logged_counts,
                    HistogramSamples::Metadata* meta,
                    HistogramSamples::Metadata* logged_meta);
 
@@ -496,9 +494,8 @@ class BASE_EXPORT CustomHistogram : public Histogram {
   static std::unique_ptr<HistogramBase> PersistentCreate(
       const std::string& name,
       const BucketRanges* ranges,
-      HistogramBase::AtomicCount* counts,
-      HistogramBase::AtomicCount* logged_counts,
-      uint32_t counts_size,
+      const DelayedPersistentAllocation& counts,
+      const DelayedPersistentAllocation& logged_counts,
       HistogramSamples::Metadata* meta,
       HistogramSamples::Metadata* logged_meta);
 
@@ -521,9 +518,8 @@ class BASE_EXPORT CustomHistogram : public Histogram {
 
   CustomHistogram(const std::string& name,
                   const BucketRanges* ranges,
-                  HistogramBase::AtomicCount* counts,
-                  HistogramBase::AtomicCount* logged_counts,
-                  uint32_t counts_size,
+                  const DelayedPersistentAllocation& counts,
+                  const DelayedPersistentAllocation& logged_counts,
                   HistogramSamples::Metadata* meta,
                   HistogramSamples::Metadata* logged_meta);