Connect SparseHistogram with the rest of stats system

With this CL, SparseHistogram is usable with SparseHistogram::FactoryGet.
Next step is to implement a Histogram like macro and implement WriteHTMLGraph
and WriteAscii to have a nice output.

BUG=139612


Review URL: https://chromiumcodereview.appspot.com/12207058

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@185451 0039d316-1c4b-4281-b951-d872f2087c98

12 files changed, 96 insertions, 94 deletions

diff --git a/base/metrics/histogram.cc b/base/metrics/histogram.cc
index 2e94841..1f26829 100644
--- a/base/metrics/histogram.cc
+++ b/base/metrics/histogram.cc
@@ -84,29 +84,6 @@ typedef HistogramBase::Sample Sample;
 // static
 const size_t Histogram::kBucketCount_MAX = 16384u;
 
-// TODO(rtenneti): delete this code after debugging.
-void CheckCorruption(const Histogram& histogram, bool new_histogram) {
-  const std::string& histogram_name = histogram.histogram_name();
-  char histogram_name_buf[128];
-  base::strlcpy(histogram_name_buf,
-                histogram_name.c_str(),
-                arraysize(histogram_name_buf));
-  base::debug::Alias(histogram_name_buf);
-
-  bool debug_new_histogram[1];
-  debug_new_histogram[0] = new_histogram;
-  base::debug::Alias(debug_new_histogram);
-
-  Sample previous_range = -1;  // Bottom range is always 0.
-  for (size_t index = 0; index < histogram.bucket_count(); ++index) {
-    int new_range = histogram.ranges(index);
-    CHECK_LT(previous_range, new_range);
-    previous_range = new_range;
-  }
-
-  CHECK(histogram.bucket_ranges()->HasValidChecksum());
-}
-
 HistogramBase* Histogram::FactoryGet(const string& name,
                                      Sample minimum,
                                      Sample maximum,
@@ -116,7 +93,7 @@ HistogramBase* Histogram::FactoryGet(const string& name,
       InspectConstructionArguments(name, &minimum, &maximum, &bucket_count);
   DCHECK(valid_arguments);
 
-  Histogram* histogram = StatisticsRecorder::FindHistogram(name);
+  HistogramBase* histogram = StatisticsRecorder::FindHistogram(name);
   if (!histogram) {
     // To avoid racy destruction at shutdown, the following will be leaked.
     BucketRanges* ranges = new BucketRanges(bucket_count + 1);
@@ -126,16 +103,13 @@ HistogramBase* Histogram::FactoryGet(const string& name,
 
     Histogram* tentative_histogram =
         new Histogram(name, minimum, maximum, bucket_count, registered_ranges);
-    CheckCorruption(*tentative_histogram, true);
 
     tentative_histogram->SetFlags(flags);
     histogram =
         StatisticsRecorder::RegisterOrDeleteDuplicate(tentative_histogram);
   }
-  // TODO(rtenneti): delete this code after debugging.
-  CheckCorruption(*histogram, false);
 
-  CHECK_EQ(HISTOGRAM, histogram->GetHistogramType());
+  DCHECK_EQ(HISTOGRAM, histogram->GetHistogramType());
   CHECK(histogram->HasConstructionArguments(minimum, maximum, bucket_count));
   return histogram;
 }
@@ -200,8 +174,7 @@ void Histogram::InitializeBucketRanges(Sample minimum,
 // static
 const int Histogram::kCommonRaceBasedCountMismatch = 5;
 
-Histogram::Inconsistencies Histogram::FindCorruption(
-    const HistogramSamples& samples) const {
+int Histogram::FindCorruption(const HistogramSamples& samples) const {
   int inconsistencies = NO_INCONSISTENCIES;
   Sample previous_range = -1;  // Bottom range is always 0.
   for (size_t index = 0; index < bucket_count(); ++index) {
@@ -230,7 +203,7 @@ Histogram::Inconsistencies Histogram::FindCorruption(
         inconsistencies |= COUNT_LOW_ERROR;
     }
   }
-  return static_cast<Inconsistencies>(inconsistencies);
+  return inconsistencies;
 }
 
 Sample Histogram::ranges(size_t i) const {
@@ -599,7 +572,7 @@ HistogramBase* LinearHistogram::FactoryGetWithRangeDescription(
       name, &minimum, &maximum, &bucket_count);
   DCHECK(valid_arguments);
 
-  Histogram* histogram = StatisticsRecorder::FindHistogram(name);
+  HistogramBase* histogram = StatisticsRecorder::FindHistogram(name);
   if (!histogram) {
     // To avoid racy destruction at shutdown, the following will be leaked.
     BucketRanges* ranges = new BucketRanges(bucket_count + 1);
@@ -610,7 +583,6 @@ HistogramBase* LinearHistogram::FactoryGetWithRangeDescription(
     LinearHistogram* tentative_histogram =
         new LinearHistogram(name, minimum, maximum, bucket_count,
                             registered_ranges);
-    CheckCorruption(*tentative_histogram, true);
 
     // Set range descriptions.
     if (descriptions) {
@@ -624,10 +596,8 @@ HistogramBase* LinearHistogram::FactoryGetWithRangeDescription(
     histogram =
         StatisticsRecorder::RegisterOrDeleteDuplicate(tentative_histogram);
   }
-  // TODO(rtenneti): delete this code after debugging.
-  CheckCorruption(*histogram, false);
 
-  CHECK_EQ(LINEAR_HISTOGRAM, histogram->GetHistogramType());
+  DCHECK_EQ(LINEAR_HISTOGRAM, histogram->GetHistogramType());
   CHECK(histogram->HasConstructionArguments(minimum, maximum, bucket_count));
   return histogram;
 }
@@ -710,7 +680,7 @@ HistogramBase* LinearHistogram::DeserializeInfoImpl(PickleIterator* iter) {
 //------------------------------------------------------------------------------
 
 HistogramBase* BooleanHistogram::FactoryGet(const string& name, int32 flags) {
-  Histogram* histogram = StatisticsRecorder::FindHistogram(name);
+  HistogramBase* histogram = StatisticsRecorder::FindHistogram(name);
   if (!histogram) {
     // To avoid racy destruction at shutdown, the following will be leaked.
     BucketRanges* ranges = new BucketRanges(4);
@@ -720,16 +690,13 @@ HistogramBase* BooleanHistogram::FactoryGet(const string& name, int32 flags) {
 
     BooleanHistogram* tentative_histogram =
         new BooleanHistogram(name, registered_ranges);
-    CheckCorruption(*tentative_histogram, true);
 
     tentative_histogram->SetFlags(flags);
     histogram =
         StatisticsRecorder::RegisterOrDeleteDuplicate(tentative_histogram);
   }
-  // TODO(rtenneti): delete this code after debugging.
-  CheckCorruption(*histogram, false);
 
-  CHECK_EQ(BOOLEAN_HISTOGRAM, histogram->GetHistogramType());
+  DCHECK_EQ(BOOLEAN_HISTOGRAM, histogram->GetHistogramType());
   return histogram;
 }
 
@@ -772,7 +739,7 @@ HistogramBase* CustomHistogram::FactoryGet(const string& name,
                                            int32 flags) {
   CHECK(ValidateCustomRanges(custom_ranges));
 
-  Histogram* histogram = StatisticsRecorder::FindHistogram(name);
+  HistogramBase* histogram = StatisticsRecorder::FindHistogram(name);
   if (!histogram) {
     BucketRanges* ranges = CreateBucketRangesFromCustomRanges(custom_ranges);
     const BucketRanges* registered_ranges =
@@ -781,17 +748,14 @@ HistogramBase* CustomHistogram::FactoryGet(const string& name,
     // To avoid racy destruction at shutdown, the following will be leaked.
     CustomHistogram* tentative_histogram =
         new CustomHistogram(name, registered_ranges);
-    CheckCorruption(*tentative_histogram, true);
 
     tentative_histogram->SetFlags(flags);
 
     histogram =
         StatisticsRecorder::RegisterOrDeleteDuplicate(tentative_histogram);
   }
-  // TODO(rtenneti): delete this code after debugging.
-  CheckCorruption(*histogram, false);
 
-  CHECK_EQ(histogram->GetHistogramType(), CUSTOM_HISTOGRAM);
+  DCHECK_EQ(histogram->GetHistogramType(), CUSTOM_HISTOGRAM);
   return histogram;
 }
 
diff --git a/base/metrics/histogram.h b/base/metrics/histogram.h
index 47db608..fe7b794 100644
--- a/base/metrics/histogram.h
+++ b/base/metrics/histogram.h
@@ -369,16 +369,6 @@ class BASE_EXPORT Histogram : public HistogramBase {
 
   typedef std::vector<Count> Counts;
 
-  enum Inconsistencies {
-    NO_INCONSISTENCIES = 0x0,
-    RANGE_CHECKSUM_ERROR = 0x1,
-    BUCKET_ORDER_ERROR = 0x2,
-    COUNT_HIGH_ERROR = 0x4,
-    COUNT_LOW_ERROR = 0x8,
-
-    NEVER_EXCEEDED_VALUE = 0x10
-  };
-
   //----------------------------------------------------------------------------
   // For a valid histogram, input should follow these restrictions:
   // minimum > 0 (if a minimum below 1 is specified, it will implicitly be
@@ -423,7 +413,7 @@ class BASE_EXPORT Histogram : public HistogramBase {
   // produce a false-alarm if a race occurred in the reading of the data during
   // a SnapShot process, but should otherwise be false at all times (unless we
   // have memory over-writes, or DRAM failures).
-  virtual Inconsistencies FindCorruption(const HistogramSamples& samples) const;
+  virtual int FindCorruption(const HistogramSamples& samples) const OVERRIDE;
 
   //----------------------------------------------------------------------------
   // Accessors for factory constuction, serialization and testing.
diff --git a/base/metrics/histogram_base.cc b/base/metrics/histogram_base.cc
index 403303a..835a05b 100644
--- a/base/metrics/histogram_base.cc
+++ b/base/metrics/histogram_base.cc
@@ -100,6 +100,11 @@ bool HistogramBase::SerializeInfo(Pickle* pickle) const {
   return SerializeInfoImpl(pickle);
 }
 
+int HistogramBase::FindCorruption(const HistogramSamples& samples) const {
+  // Not supported by default.
+  return NO_INCONSISTENCIES;
+}
+
 void HistogramBase::WriteJSON(std::string* output) const {
   Count count;
   scoped_ptr<ListValue> buckets(new ListValue());
diff --git a/base/metrics/histogram_base.h b/base/metrics/histogram_base.h
index 729670c..12d126d 100644
--- a/base/metrics/histogram_base.h
+++ b/base/metrics/histogram_base.h
@@ -70,6 +70,17 @@ class BASE_EXPORT HistogramBase {
     kHexRangePrintingFlag = 0x8000,
   };
 
+  // Histogram data inconsistency types.
+  enum Inconsistency {
+    NO_INCONSISTENCIES = 0x0,
+    RANGE_CHECKSUM_ERROR = 0x1,
+    BUCKET_ORDER_ERROR = 0x2,
+    COUNT_HIGH_ERROR = 0x4,
+    COUNT_LOW_ERROR = 0x8,
+
+    NEVER_EXCEEDED_VALUE = 0x10
+  };
+
   explicit HistogramBase(const std::string& name);
   virtual ~HistogramBase();
 
@@ -103,6 +114,10 @@ class BASE_EXPORT HistogramBase {
   // does not serialize the samples.
   bool SerializeInfo(Pickle* pickle) const;
 
+  // Try to find out data corruption from histogram and the samples.
+  // The returned value is a combination of Inconsistency enum.
+  virtual int FindCorruption(const HistogramSamples& samples) const;
+
   // Snapshot the current complete set of sample data.
   // Override with atomic/locked snapshot if needed.
   virtual scoped_ptr<HistogramSamples> SnapshotSamples() const = 0;
diff --git a/base/metrics/histogram_base_unittest.cc b/base/metrics/histogram_base_unittest.cc
index 4944f31..0e19d56 100644
--- a/base/metrics/histogram_base_unittest.cc
+++ b/base/metrics/histogram_base_unittest.cc
@@ -167,6 +167,25 @@ TEST_F(HistogramBaseTest, DeserializeCustomHistogram) {
   EXPECT_EQ(0, deserialized->flags());
 }
 
-// TODO(kaiwang): Add SparseHistogram test.
+TEST_F(HistogramBaseTest, DeserializeSparseHistogram) {
+  HistogramBase* histogram = SparseHistogram::FactoryGet(
+      "TestHistogram", HistogramBase::kIPCSerializationSourceFlag);
+
+  Pickle pickle;
+  ASSERT_TRUE(histogram->SerializeInfo(&pickle));
+
+  PickleIterator iter(pickle);
+  HistogramBase* deserialized = DeserializeHistogramInfo(&iter);
+  EXPECT_EQ(histogram, deserialized);
+
+  ResetStatisticsRecorder();
+
+  PickleIterator iter2(pickle);
+  deserialized = DeserializeHistogramInfo(&iter2);
+  EXPECT_TRUE(deserialized);
+  EXPECT_NE(histogram, deserialized);
+  EXPECT_EQ("TestHistogram", deserialized->histogram_name());
+  EXPECT_EQ(0, deserialized->flags());
+}
 
 }  // namespace base
diff --git a/base/metrics/histogram_flattener.h b/base/metrics/histogram_flattener.h
index 137ce98..ca05a4f 100644
--- a/base/metrics/histogram_flattener.h
+++ b/base/metrics/histogram_flattener.h
@@ -24,14 +24,14 @@ class BASE_EXPORT HistogramFlattener {
   virtual void RecordDelta(const HistogramBase& histogram,
                            const HistogramSamples& snapshot) = 0;
 
-  // Will be called each time a type of Inconsistenies is seen on a histogram,
+  // Will be called each time a type of Inconsistency is seen on a histogram,
   // during inspections done internally in HistogramSnapshotManager class.
-  virtual void InconsistencyDetected(Histogram::Inconsistencies problem) = 0;
+  virtual void InconsistencyDetected(HistogramBase::Inconsistency problem) = 0;
 
-  // Will be called when a type of Inconsistenies is seen for the first time
-  // on a histogram.
+  // Will be called when a type of Inconsistency is seen for the first time on
+  // a histogram.
   virtual void UniqueInconsistencyDetected(
-      Histogram::Inconsistencies problem) = 0;
+      HistogramBase::Inconsistency problem) = 0;
 
   // Will be called when the total logged sample count of a histogram
   // differs from the sum of logged sample count in all the buckets.  The
diff --git a/base/metrics/histogram_snapshot_manager.cc b/base/metrics/histogram_snapshot_manager.cc
index ad054b1..2301819 100644
--- a/base/metrics/histogram_snapshot_manager.cc
+++ b/base/metrics/histogram_snapshot_manager.cc
@@ -25,7 +25,7 @@ HistogramSnapshotManager::~HistogramSnapshotManager() {
   STLDeleteValues(&logged_samples_);
 }
 
-void HistogramSnapshotManager::PrepareDeltas(Histogram::Flags flag_to_set,
+void HistogramSnapshotManager::PrepareDeltas(HistogramBase::Flags flag_to_set,
                                              bool record_only_uma) {
   StatisticsRecorder::Histograms histograms;
   StatisticsRecorder::GetHistograms(&histograms);
@@ -40,7 +40,7 @@ void HistogramSnapshotManager::PrepareDeltas(Histogram::Flags flag_to_set,
   }
 }
 
-void HistogramSnapshotManager::PrepareDelta(const Histogram& histogram) {
+void HistogramSnapshotManager::PrepareDelta(const HistogramBase& histogram) {
   DCHECK(histogram_flattener_);
 
   // Get up-to-date snapshot of sample stats.
@@ -52,13 +52,13 @@ void HistogramSnapshotManager::PrepareDelta(const Histogram& histogram) {
   // Crash if we detect that our histograms have been overwritten.  This may be
   // a fair distance from the memory smasher, but we hope to correlate these
   // crashes with other events, such as plugins, or usage patterns, etc.
-  if (Histogram::BUCKET_ORDER_ERROR & corruption) {
+  if (HistogramBase::BUCKET_ORDER_ERROR & corruption) {
     // The checksum should have caught this, so crash separately if it didn't.
-    CHECK_NE(0, Histogram::RANGE_CHECKSUM_ERROR & corruption);
+    CHECK_NE(0, HistogramBase::RANGE_CHECKSUM_ERROR & corruption);
     CHECK(false);  // Crash for the bucket order corruption.
   }
   // Checksum corruption might not have caused order corruption.
-  CHECK_EQ(0, Histogram::RANGE_CHECKSUM_ERROR & corruption);
+  CHECK_EQ(0, HistogramBase::RANGE_CHECKSUM_ERROR & corruption);
 
   // Note, at this point corruption can only be COUNT_HIGH_ERROR or
   // COUNT_LOW_ERROR and they never arise together, so we don't need to extract
@@ -67,14 +67,14 @@ void HistogramSnapshotManager::PrepareDelta(const Histogram& histogram) {
     DLOG(ERROR) << "Histogram: " << histogram_name
                 << " has data corruption: " << corruption;
     histogram_flattener_->InconsistencyDetected(
-        static_cast<Histogram::Inconsistencies>(corruption));
+        static_cast<HistogramBase::Inconsistency>(corruption));
     // Don't record corrupt data to metrics services.
     int old_corruption = inconsistencies_[histogram_name];
     if (old_corruption == (corruption | old_corruption))
       return;  // We've already seen this corruption for this histogram.
     inconsistencies_[histogram_name] |= corruption;
     histogram_flattener_->UniqueInconsistencyDetected(
-        static_cast<Histogram::Inconsistencies>(corruption));
+        static_cast<HistogramBase::Inconsistency>(corruption));
     return;
   }
 
diff --git a/base/metrics/histogram_snapshot_manager.h b/base/metrics/histogram_snapshot_manager.h
index 0ec1ac3..3c70508 100644
--- a/base/metrics/histogram_snapshot_manager.h
+++ b/base/metrics/histogram_snapshot_manager.h
@@ -9,7 +9,7 @@
 #include <string>
 
 #include "base/basictypes.h"
-#include "base/metrics/histogram.h"
+#include "base/metrics/histogram_base.h"
 
 namespace base {
 
@@ -31,11 +31,11 @@ class BASE_EXPORT HistogramSnapshotManager {
   // Snapshot all histograms, and ask |histogram_flattener_| to record the
   // delta. The arguments allow selecting only a subset of histograms for
   // recording, or to set a flag in each recorded histogram.
-  void PrepareDeltas(Histogram::Flags flags_to_set, bool record_only_uma);
+  void PrepareDeltas(HistogramBase::Flags flags_to_set, bool record_only_uma);
 
  private:
   // Snapshot this histogram, and record the delta.
-  void PrepareDelta(const Histogram& histogram);
+  void PrepareDelta(const HistogramBase& histogram);
 
   // Try to detect and fix count inconsistency of logged samples.
   void InspectLoggedSamplesInconsistency(
diff --git a/base/metrics/histogram_unittest.cc b/base/metrics/histogram_unittest.cc
index 27c0faf..b5081b6 100644
--- a/base/metrics/histogram_unittest.cc
+++ b/base/metrics/histogram_unittest.cc
@@ -315,21 +315,21 @@ TEST_F(HistogramTest, CorruptSampleCounts) {
   histogram->Add(40);
 
   scoped_ptr<SampleVector> snapshot = histogram->SnapshotSampleVector();
-  EXPECT_EQ(Histogram::NO_INCONSISTENCIES,
+  EXPECT_EQ(HistogramBase::NO_INCONSISTENCIES,
             histogram->FindCorruption(*snapshot));
   EXPECT_EQ(2, snapshot->redundant_count());
   EXPECT_EQ(2, snapshot->TotalCount());
 
   snapshot->counts_[3] += 100;  // Sample count won't match redundant count.
-  EXPECT_EQ(Histogram::COUNT_LOW_ERROR,
+  EXPECT_EQ(HistogramBase::COUNT_LOW_ERROR,
             histogram->FindCorruption(*snapshot));
   snapshot->counts_[2] -= 200;
-  EXPECT_EQ(Histogram::COUNT_HIGH_ERROR,
+  EXPECT_EQ(HistogramBase::COUNT_HIGH_ERROR,
             histogram->FindCorruption(*snapshot));
 
   // But we can't spot a corruption if it is compensated for.
   snapshot->counts_[1] += 100;
-  EXPECT_EQ(Histogram::NO_INCONSISTENCIES,
+  EXPECT_EQ(HistogramBase::NO_INCONSISTENCIES,
             histogram->FindCorruption(*snapshot));
 }
 
@@ -338,7 +338,7 @@ TEST_F(HistogramTest, CorruptBucketBounds) {
       Histogram::FactoryGet("Histogram", 1, 64, 8, HistogramBase::kNoFlags));
 
   scoped_ptr<SampleVector> snapshot = histogram->SnapshotSampleVector();
-  EXPECT_EQ(Histogram::NO_INCONSISTENCIES,
+  EXPECT_EQ(HistogramBase::NO_INCONSISTENCIES,
             histogram->FindCorruption(*snapshot));
 
   BucketRanges* bucket_ranges =
@@ -346,8 +346,9 @@ TEST_F(HistogramTest, CorruptBucketBounds) {
   HistogramBase::Sample tmp = bucket_ranges->range(1);
   bucket_ranges->set_range(1, bucket_ranges->range(2));
   bucket_ranges->set_range(2, tmp);
-  EXPECT_EQ(Histogram::BUCKET_ORDER_ERROR | Histogram::RANGE_CHECKSUM_ERROR,
-            histogram->FindCorruption(*snapshot));
+  EXPECT_EQ(
+      HistogramBase::BUCKET_ORDER_ERROR | HistogramBase::RANGE_CHECKSUM_ERROR,
+      histogram->FindCorruption(*snapshot));
 
   bucket_ranges->set_range(2, bucket_ranges->range(1));
   bucket_ranges->set_range(1, tmp);
@@ -355,11 +356,11 @@ TEST_F(HistogramTest, CorruptBucketBounds) {
 
   // Show that two simple changes don't offset each other
   bucket_ranges->set_range(3, bucket_ranges->range(3) + 1);
-  EXPECT_EQ(Histogram::RANGE_CHECKSUM_ERROR,
+  EXPECT_EQ(HistogramBase::RANGE_CHECKSUM_ERROR,
             histogram->FindCorruption(*snapshot));
 
   bucket_ranges->set_range(4, bucket_ranges->range(4) - 1);
-  EXPECT_EQ(Histogram::RANGE_CHECKSUM_ERROR,
+  EXPECT_EQ(HistogramBase::RANGE_CHECKSUM_ERROR,
             histogram->FindCorruption(*snapshot));
 
   // Repair histogram so that destructor won't DCHECK().
diff --git a/base/metrics/sparse_histogram.cc b/base/metrics/sparse_histogram.cc
index c64f7cb..2952673 100644
--- a/base/metrics/sparse_histogram.cc
+++ b/base/metrics/sparse_histogram.cc
@@ -19,9 +19,16 @@ typedef HistogramBase::Sample Sample;
 
 // static
 HistogramBase* SparseHistogram::FactoryGet(const string& name, int32 flags) {
-  // TODO(kaiwang): Register and get SparseHistogram with StatisticsRecorder.
-  HistogramBase* histogram = new SparseHistogram(name);
-  histogram->SetFlags(flags);
+  HistogramBase* histogram = StatisticsRecorder::FindHistogram(name);
+
+  if (!histogram) {
+    // To avoid racy destruction at shutdown, the following will be leaked.
+    HistogramBase* tentative_histogram = new SparseHistogram(name);
+    tentative_histogram->SetFlags(flags);
+    histogram =
+        StatisticsRecorder::RegisterOrDeleteDuplicate(tentative_histogram);
+  }
+  DCHECK_EQ(SPARSE_HISTOGRAM, histogram->GetHistogramType());
   return histogram;
 }
 
diff --git a/base/metrics/statistics_recorder.cc b/base/metrics/statistics_recorder.cc
index 39a6275..f6174f3 100644
--- a/base/metrics/statistics_recorder.cc
+++ b/base/metrics/statistics_recorder.cc
@@ -45,7 +45,8 @@ bool StatisticsRecorder::IsActive() {
 }
 
 // static
-Histogram* StatisticsRecorder::RegisterOrDeleteDuplicate(Histogram* histogram) {
+HistogramBase* StatisticsRecorder::RegisterOrDeleteDuplicate(
+    HistogramBase* histogram) {
   // As per crbug.com/79322 the histograms are intentionally leaked, so we need
   // to annotate them. Because ANNOTATE_LEAKING_OBJECT_PTR may be used only once
   // for an object, the duplicates should not be annotated.
@@ -56,8 +57,8 @@ Histogram* StatisticsRecorder::RegisterOrDeleteDuplicate(Histogram* histogram) {
     return histogram;
   }
 
-  Histogram* histogram_to_delete = NULL;
-  Histogram* histogram_to_return = NULL;
+  HistogramBase* histogram_to_delete = NULL;
+  HistogramBase* histogram_to_return = NULL;
   {
     base::AutoLock auto_lock(*lock_);
     if (histograms_ == NULL) {
@@ -254,7 +255,7 @@ void StatisticsRecorder::GetBucketRanges(
 }
 
 // static
-Histogram* StatisticsRecorder::FindHistogram(const std::string& name) {
+HistogramBase* StatisticsRecorder::FindHistogram(const std::string& name) {
   if (lock_ == NULL)
     return NULL;
   base::AutoLock auto_lock(*lock_);
diff --git a/base/metrics/statistics_recorder.h b/base/metrics/statistics_recorder.h
index 6d40aff..4bb2548 100644
--- a/base/metrics/statistics_recorder.h
+++ b/base/metrics/statistics_recorder.h
@@ -23,12 +23,12 @@
 namespace base {
 
 class BucketRanges;
-class Histogram;
+class HistogramBase;
 class Lock;
 
 class BASE_EXPORT StatisticsRecorder {
  public:
-  typedef std::vector<Histogram*> Histograms;
+  typedef std::vector<HistogramBase*> Histograms;
 
   // Initializes the StatisticsRecorder system.
   static void Initialize();
@@ -40,7 +40,7 @@ class BASE_EXPORT StatisticsRecorder {
   // identically named histogram is already registered, then the argument
   // |histogram| will deleted.  The returned value is always the registered
   // histogram (either the argument, or the pre-existing registered histogram).
-  static Histogram* RegisterOrDeleteDuplicate(Histogram* histogram);
+  static HistogramBase* RegisterOrDeleteDuplicate(HistogramBase* histogram);
 
   // Register, or add a new BucketRanges. If an identically BucketRanges is
   // already registered, then the argument |ranges| will deleted. The returned
@@ -68,7 +68,7 @@ class BASE_EXPORT StatisticsRecorder {
 
   // Find a histogram by name. It matches the exact name. This method is thread
   // safe.  It returns NULL if a matching histogram is not found.
-  static Histogram* FindHistogram(const std::string& name);
+  static HistogramBase* FindHistogram(const std::string& name);
 
   static bool dump_on_exit() { return dump_on_exit_; }
 
@@ -82,7 +82,7 @@ class BASE_EXPORT StatisticsRecorder {
 
  private:
   // We keep all registered histograms in a map, from name to histogram.
-  typedef std::map<std::string, Histogram*> HistogramMap;
+  typedef std::map<std::string, HistogramBase*> HistogramMap;
 
   // We keep all |bucket_ranges_| in a map, from checksum to a list of
   // |bucket_ranges_|.  Checksum is calculated from the |ranges_| in