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

30 files changed, 166 insertions, 158 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
diff --git a/chrome/browser/chrome_browser_application_mac_unittest.mm b/chrome/browser/chrome_browser_application_mac_unittest.mm
index 98141674..9c31806 100644
--- a/chrome/browser/chrome_browser_application_mac_unittest.mm
+++ b/chrome/browser/chrome_browser_application_mac_unittest.mm
@@ -12,7 +12,7 @@
 #import "chrome/browser/chrome_browser_application_mac.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
-using base::Histogram;
+using base::HistogramBase;
 using base::HistogramSamples;
 using base::StatisticsRecorder;
 
@@ -76,7 +76,7 @@ TEST(ChromeApplicationMacTest, RecordException) {
   // We should have exactly the right number of exceptions.
   StatisticsRecorder::GetSnapshot("OSX.NSException", &histograms);
   EXPECT_EQ(1U, histograms.size());
-  EXPECT_EQ(Histogram::kUmaTargetedHistogramFlag, histograms[0]->flags());
+  EXPECT_EQ(HistogramBase::kUmaTargetedHistogramFlag, histograms[0]->flags());
 
   scoped_ptr<HistogramSamples> samples(histograms[0]->SnapshotSamples());
   EXPECT_EQ(4, samples->GetCount(0));
@@ -85,7 +85,9 @@ TEST(ChromeApplicationMacTest, RecordException) {
   EXPECT_EQ(2, samples->GetCount(3));
 
   // The unknown exceptions should end up in the overflow bucket.
-  EXPECT_EQ(kUnknownNSException + 1, histograms[0]->bucket_count());
+  EXPECT_TRUE(histograms[0]->HasConstructionArguments(1,
+                                                      kUnknownNSException,
+                                                      kUnknownNSException + 1));
   EXPECT_EQ(4, samples->GetCount(kUnknownNSException));
 }
 
diff --git a/chrome/browser/extensions/api/metrics_private/metrics_apitest.cc b/chrome/browser/extensions/api/metrics_private/metrics_apitest.cc
index e9d5efe..407ddaa 100644
--- a/chrome/browser/extensions/api/metrics_private/metrics_apitest.cc
+++ b/chrome/browser/extensions/api/metrics_private/metrics_apitest.cc
@@ -110,13 +110,12 @@ void ValidateHistograms(const RecordedHistogram* recorded,
     const RecordedHistogram& r = recorded[i];
     size_t j = 0;
     for (j = 0; j < histograms.size(); ++j) {
-      base::Histogram* histogram(histograms[j]);
+      base::HistogramBase* histogram(histograms[j]);
 
       if (r.name == histogram->histogram_name()) {
         EXPECT_EQ(r.type, histogram->GetHistogramType());
-        EXPECT_EQ(r.min, histogram->declared_min());
-        EXPECT_EQ(r.max, histogram->declared_max());
-        EXPECT_EQ(r.buckets, histogram->bucket_count());
+        EXPECT_TRUE(
+            histogram->HasConstructionArguments(r.min, r.max, r.buckets));
         break;
       }
     }
diff --git a/chrome/browser/net/http_pipelining_compatibility_client_unittest.cc b/chrome/browser/net/http_pipelining_compatibility_client_unittest.cc
index 04dddfe..7f33790 100644
--- a/chrome/browser/net/http_pipelining_compatibility_client_unittest.cc
+++ b/chrome/browser/net/http_pipelining_compatibility_client_unittest.cc
@@ -25,7 +25,7 @@
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
-using base::Histogram;
+using base::HistogramBase;
 using base::HistogramSamples;
 
 namespace chrome_browser_net {
@@ -210,8 +210,8 @@ class HttpPipeliningCompatibilityClientTest : public testing::Test {
  private:
   scoped_ptr<HistogramSamples> GetHistogram(const char* name) {
     scoped_ptr<HistogramSamples> samples;
-    Histogram* cached_histogram = NULL;
-    Histogram* current_histogram =
+    HistogramBase* cached_histogram = NULL;
+    HistogramBase* current_histogram =
         base::StatisticsRecorder::FindHistogram(name);
     if (ContainsKey(histograms_, name)) {
       cached_histogram = histograms_[name];
@@ -238,12 +238,12 @@ class HttpPipeliningCompatibilityClientTest : public testing::Test {
     return samples.Pass();
   }
 
-  static std::map<std::string, Histogram*> histograms_;
+  static std::map<std::string, HistogramBase*> histograms_;
   std::map<std::string, HistogramSamples*> original_samples_;
 };
 
 // static
-std::map<std::string, Histogram*>
+std::map<std::string, HistogramBase*>
     HttpPipeliningCompatibilityClientTest::histograms_;
 
 TEST_F(HttpPipeliningCompatibilityClientTest, Success) {
diff --git a/chrome/browser/spellchecker/spellcheck_host_metrics_unittest.cc b/chrome/browser/spellchecker/spellcheck_host_metrics_unittest.cc
index 8614d53..38977ba 100644
--- a/chrome/browser/spellchecker/spellcheck_host_metrics_unittest.cc
+++ b/chrome/browser/spellchecker/spellcheck_host_metrics_unittest.cc
@@ -13,7 +13,7 @@
 #include "base/utf_string_conversions.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
-using base::Histogram;
+using base::HistogramBase;
 using base::HistogramSamples;
 using base::StatisticsRecorder;
 
@@ -37,7 +37,7 @@ class SpellcheckHostMetricsTest : public testing::Test {
 
 TEST_F(SpellcheckHostMetricsTest, RecordEnabledStats) {
   scoped_ptr<HistogramSamples> baseline;
-  Histogram* histogram =
+  HistogramBase* histogram =
       StatisticsRecorder::FindHistogram("SpellCheck.Enabled");
   if (histogram)
     baseline = histogram->SnapshotSamples();
@@ -69,7 +69,7 @@ TEST_F(SpellcheckHostMetricsTest, RecordEnabledStats) {
 TEST_F(SpellcheckHostMetricsTest, CustomWordStats) {
   metrics()->RecordCustomWordCountStats(123);
 
-  Histogram* histogram =
+  HistogramBase* histogram =
       StatisticsRecorder::FindHistogram("SpellCheck.CustomWords");
   ASSERT_TRUE(histogram != NULL);
   scoped_ptr<HistogramSamples> baseline = histogram->SnapshotSamples();
@@ -102,7 +102,7 @@ TEST_F(SpellcheckHostMetricsTest, RecordWordCountsDiscardsDuplicates) {
   // Get baselines for all affected histograms.
   scoped_ptr<HistogramSamples> baselines[arraysize(histogramName)];
   for (size_t i = 0; i < arraysize(histogramName); ++i) {
-    Histogram* histogram =
+    HistogramBase* histogram =
         StatisticsRecorder::FindHistogram(histogramName[i]);
     if (histogram)
       baselines[i] = histogram->SnapshotSamples();
@@ -114,7 +114,7 @@ TEST_F(SpellcheckHostMetricsTest, RecordWordCountsDiscardsDuplicates) {
   // Get samples for all affected histograms.
   scoped_ptr<HistogramSamples> samples[arraysize(histogramName)];
   for (size_t i = 0; i < arraysize(histogramName); ++i) {
-    Histogram* histogram =
+    HistogramBase* histogram =
         StatisticsRecorder::FindHistogram(histogramName[i]);
     ASSERT_TRUE(histogram != NULL);
     samples[i] = histogram->SnapshotSamples();
@@ -128,8 +128,7 @@ TEST_F(SpellcheckHostMetricsTest, RecordWordCountsDiscardsDuplicates) {
 TEST_F(SpellcheckHostMetricsTest, RecordSpellingServiceStats) {
   const char kMetricName[] = "SpellCheck.SpellingService.Enabled";
   scoped_ptr<HistogramSamples> baseline;
-  Histogram* histogram =
-      StatisticsRecorder::FindHistogram(kMetricName);
+  HistogramBase* histogram = StatisticsRecorder::FindHistogram(kMetricName);
   if (histogram)
     baseline = histogram->SnapshotSamples();
 
diff --git a/chrome/browser/ui/cocoa/browser/password_generation_bubble_controller_unittest.mm b/chrome/browser/ui/cocoa/browser/password_generation_bubble_controller_unittest.mm
index 55c4e72..0ac11eb 100644
--- a/chrome/browser/ui/cocoa/browser/password_generation_bubble_controller_unittest.mm
+++ b/chrome/browser/ui/cocoa/browser/password_generation_bubble_controller_unittest.mm
@@ -14,7 +14,7 @@
 #include "content/public/common/password_form.h"
 #include "testing/gtest_mac.h"
 
-using base::Histogram;
+using base::HistogramBase;
 using base::HistogramSamples;
 using base::StatisticsRecorder;
 
@@ -34,7 +34,8 @@ class PasswordGenerationBubbleControllerTest : public CocoaProfileTest {
 
     generator_.reset(new autofill::PasswordGenerator(20));
 
-    Histogram* histogram = StatisticsRecorder::FindHistogram(kHistogramName);
+    HistogramBase* histogram =
+        StatisticsRecorder::FindHistogram(kHistogramName);
     if (histogram)
       original_ = histogram->SnapshotSamples();
 
@@ -65,7 +66,7 @@ class PasswordGenerationBubbleControllerTest : public CocoaProfileTest {
   }
 
   HistogramSamples* GetHistogramSamples() {
-    Histogram* histogram =
+    HistogramBase* histogram =
         StatisticsRecorder::FindHistogram(kHistogramName);
     if (histogram) {
       current_ = histogram->SnapshotSamples();
diff --git a/chrome/common/metrics/metrics_service_base.cc b/chrome/common/metrics/metrics_service_base.cc
index bb534b1..cd400c46 100644
--- a/chrome/common/metrics/metrics_service_base.cc
+++ b/chrome/common/metrics/metrics_service_base.cc
@@ -43,15 +43,15 @@ void MetricsServiceBase::RecordDelta(
 }
 
 void MetricsServiceBase::InconsistencyDetected(
-    Histogram::Inconsistencies problem) {
+    base::HistogramBase::Inconsistency problem) {
   UMA_HISTOGRAM_ENUMERATION("Histogram.InconsistenciesBrowser",
-                            problem, Histogram::NEVER_EXCEEDED_VALUE);
+                            problem, base::HistogramBase::NEVER_EXCEEDED_VALUE);
 }
 
 void MetricsServiceBase::UniqueInconsistencyDetected(
-    Histogram::Inconsistencies problem) {
+    base::HistogramBase::Inconsistency problem) {
   UMA_HISTOGRAM_ENUMERATION("Histogram.InconsistenciesBrowserUnique",
-                            problem, Histogram::NEVER_EXCEEDED_VALUE);
+                            problem, base::HistogramBase::NEVER_EXCEEDED_VALUE);
 }
 
 void MetricsServiceBase::InconsistencyDetectedInLoggedCount(int amount) {
diff --git a/chrome/common/metrics/metrics_service_base.h b/chrome/common/metrics/metrics_service_base.h
index a40b9a2..fc75b4c 100644
--- a/chrome/common/metrics/metrics_service_base.h
+++ b/chrome/common/metrics/metrics_service_base.h
@@ -24,9 +24,9 @@ class MetricsServiceBase : public base::HistogramFlattener {
   virtual void RecordDelta(const base::HistogramBase& histogram,
                            const base::HistogramSamples& snapshot) OVERRIDE;
   virtual void InconsistencyDetected(
-      base::Histogram::Inconsistencies problem) OVERRIDE;
+      base::HistogramBase::Inconsistency problem) OVERRIDE;
   virtual void UniqueInconsistencyDetected(
-      base::Histogram::Inconsistencies problem) OVERRIDE;
+      base::HistogramBase::Inconsistency problem) OVERRIDE;
   virtual void InconsistencyDetectedInLoggedCount(int amount) OVERRIDE;
 
  protected:
diff --git a/chrome/common/startup_metric_utils.cc b/chrome/common/startup_metric_utils.cc
index 8f3bdac..0aae56c 100644
--- a/chrome/common/startup_metric_utils.cc
+++ b/chrome/common/startup_metric_utils.cc
@@ -113,7 +113,7 @@ void OnInitialPageLoadComplete() {
 
   // Set UMA flag for histograms outside chrome/ that can't use the
   // ScopedSlowStartupUMA class.
-  base::Histogram* histogram =
+  base::HistogramBase* histogram =
       base::StatisticsRecorder::FindHistogram("Startup.SlowStartupNSSInit");
   if (histogram)
     histogram->SetFlags(base::HistogramBase::kUmaTargetedHistogramFlag);
diff --git a/chrome/test/base/uma_histogram_helper.cc b/chrome/test/base/uma_histogram_helper.cc
index 8b4ff41..571f477 100644
--- a/chrome/test/base/uma_histogram_helper.cc
+++ b/chrome/test/base/uma_histogram_helper.cc
@@ -32,8 +32,9 @@ void UMAHistogramHelper::ExpectUniqueSample(
     const std::string& name,
     base::HistogramBase::Sample sample,
     base::HistogramBase::Count expected_count) {
-  base::Histogram* histogram = base::StatisticsRecorder::FindHistogram(name);
-  EXPECT_NE(static_cast<base::Histogram*>(NULL), histogram)
+  base::HistogramBase* histogram =
+      base::StatisticsRecorder::FindHistogram(name);
+  EXPECT_NE(static_cast<base::HistogramBase*>(NULL), histogram)
       << "Histogram \"" << name << "\" does not exist.";
 
   if (histogram) {
@@ -46,8 +47,9 @@ void UMAHistogramHelper::ExpectUniqueSample(
 void UMAHistogramHelper::ExpectTotalCount(
     const std::string& name,
     base::HistogramBase::Count count) {
-  base::Histogram* histogram = base::StatisticsRecorder::FindHistogram(name);
-  EXPECT_NE(static_cast<base::Histogram*>(NULL), histogram)
+  base::HistogramBase* histogram =
+      base::StatisticsRecorder::FindHistogram(name);
+  EXPECT_NE(static_cast<base::HistogramBase*>(NULL), histogram)
       << "Histogram \"" << name << "\" does not exist.";
 
   if (histogram) {
diff --git a/content/browser/histogram_message_filter.cc b/content/browser/histogram_message_filter.cc
index ef31efd..ac08af3 100644
--- a/content/browser/histogram_message_filter.cc
+++ b/content/browser/histogram_message_filter.cc
@@ -63,7 +63,8 @@ void HistogramMessageFilter::OnGetBrowserHistogram(
                << " switches.";
     return;
   }
-  base::Histogram* histogram = base::StatisticsRecorder::FindHistogram(name);
+  base::HistogramBase* histogram =
+      base::StatisticsRecorder::FindHistogram(name);
   if (!histogram) {
     *histogram_json = "{}";
   } else {
diff --git a/content/common/child_histogram_message_filter.cc b/content/common/child_histogram_message_filter.cc
index 3b410cc..25f9180 100644
--- a/content/common/child_histogram_message_filter.cc
+++ b/content/common/child_histogram_message_filter.cc
@@ -87,15 +87,15 @@ void ChildHistogramMessageFilter::RecordDelta(
 }
 
 void ChildHistogramMessageFilter::InconsistencyDetected(
-    base::Histogram::Inconsistencies problem) {
+    base::HistogramBase::Inconsistency problem) {
   UMA_HISTOGRAM_ENUMERATION("Histogram.InconsistenciesChildProcess",
-                            problem, base::Histogram::NEVER_EXCEEDED_VALUE);
+                            problem, base::HistogramBase::NEVER_EXCEEDED_VALUE);
 }
 
 void ChildHistogramMessageFilter::UniqueInconsistencyDetected(
-    base::Histogram::Inconsistencies problem) {
+    base::HistogramBase::Inconsistency problem) {
   UMA_HISTOGRAM_ENUMERATION("Histogram.InconsistenciesChildProcessUnique",
-                            problem, base::Histogram::NEVER_EXCEEDED_VALUE);
+                            problem, base::HistogramBase::NEVER_EXCEEDED_VALUE);
 }
 
 void ChildHistogramMessageFilter::InconsistencyDetectedInLoggedCount(
diff --git a/content/common/child_histogram_message_filter.h b/content/common/child_histogram_message_filter.h
index a43750a..4955d49 100644
--- a/content/common/child_histogram_message_filter.h
+++ b/content/common/child_histogram_message_filter.h
@@ -38,9 +38,9 @@ class ChildHistogramMessageFilter : public base::HistogramFlattener,
   virtual void RecordDelta(const base::HistogramBase& histogram,
                            const base::HistogramSamples& snapshot) OVERRIDE;
   virtual void InconsistencyDetected(
-      base::Histogram::Inconsistencies problem) OVERRIDE;
+      base::HistogramBase::Inconsistency problem) OVERRIDE;
   virtual void UniqueInconsistencyDetected(
-      base::Histogram::Inconsistencies problem) OVERRIDE;
+      base::HistogramBase::Inconsistency problem) OVERRIDE;
   virtual void InconsistencyDetectedInLoggedCount(int amount) OVERRIDE;
 
  private:
diff --git a/content/renderer/dom_automation_controller.cc b/content/renderer/dom_automation_controller.cc
index 38c8790..1718d64 100644
--- a/content/renderer/dom_automation_controller.cc
+++ b/content/renderer/dom_automation_controller.cc
@@ -183,7 +183,7 @@ void DomAutomationController::GetHistogram(const CppArgumentList& args,
     result->SetNull();
     return;
   }
-  base::Histogram* histogram =
+  base::HistogramBase* histogram =
       base::StatisticsRecorder::FindHistogram(args[0].ToString());
   std::string output;
   if (!histogram) {
diff --git a/dbus/signal_sender_verification_unittest.cc b/dbus/signal_sender_verification_unittest.cc
index d66067f..2f2eb44 100644
--- a/dbus/signal_sender_verification_unittest.cc
+++ b/dbus/signal_sender_verification_unittest.cc
@@ -182,7 +182,7 @@ TEST_F(SignalSenderVerificationTest, TestSignalAccepted) {
 TEST_F(SignalSenderVerificationTest, TestSignalRejected) {
   // To make sure the histogram instance is created.
   UMA_HISTOGRAM_COUNTS("DBus.RejectedSignalCount", 0);
-  base::Histogram* reject_signal_histogram =
+  base::HistogramBase* reject_signal_histogram =
         base::StatisticsRecorder::FindHistogram("DBus.RejectedSignalCount");
   scoped_ptr<base::HistogramSamples> samples1(
       reject_signal_histogram->SnapshotSamples());
diff --git a/net/disk_cache/stats_histogram.cc b/net/disk_cache/stats_histogram.cc
index 3292a20..7499ab2 100644
--- a/net/disk_cache/stats_histogram.cc
+++ b/net/disk_cache/stats_histogram.cc
@@ -45,7 +45,7 @@ StatsHistogram* StatsHistogram::FactoryGet(const std::string& name,
   Sample minimum = 1;
   Sample maximum = disk_cache::Stats::kDataSizesLength - 1;
   size_t bucket_count = disk_cache::Stats::kDataSizesLength;
-  Histogram* histogram = StatisticsRecorder::FindHistogram(name);
+  HistogramBase* histogram = StatisticsRecorder::FindHistogram(name);
   if (!histogram) {
     DCHECK(stats);
 
@@ -83,9 +83,9 @@ scoped_ptr<HistogramSamples> StatsHistogram::SnapshotSamples() const {
   return samples.PassAs<HistogramSamples>();
 }
 
-Histogram::Inconsistencies StatsHistogram::FindCorruption(
-    const HistogramSamples& samples) const {
-  return NO_INCONSISTENCIES;  // This class won't monitor inconsistencies.
+int StatsHistogram::FindCorruption(const HistogramSamples& samples) const {
+  // This class won't monitor inconsistencies.
+  return HistogramBase::NO_INCONSISTENCIES;
 }
 
 }  // namespace disk_cache
diff --git a/net/disk_cache/stats_histogram.h b/net/disk_cache/stats_histogram.h
index 6959622..09a37fd 100644
--- a/net/disk_cache/stats_histogram.h
+++ b/net/disk_cache/stats_histogram.h
@@ -43,7 +43,7 @@ class StatsHistogram : public base::Histogram {
                                     const Stats* stats);
 
   virtual scoped_ptr<base::HistogramSamples> SnapshotSamples() const OVERRIDE;
-  virtual Inconsistencies FindCorruption(
+  virtual int FindCorruption(
       const base::HistogramSamples& samples) const OVERRIDE;
 
  private:
diff --git a/net/socket_stream/socket_stream_metrics_unittest.cc b/net/socket_stream/socket_stream_metrics_unittest.cc
index 76ad495..741acb7 100644
--- a/net/socket_stream/socket_stream_metrics_unittest.cc
+++ b/net/socket_stream/socket_stream_metrics_unittest.cc
@@ -14,6 +14,7 @@
 #include "testing/platform_test.h"
 
 using base::Histogram;
+using base::HistogramBase;
 using base::HistogramSamples;
 using base::StatisticsRecorder;
 
@@ -24,7 +25,7 @@ TEST(SocketStreamMetricsTest, ProtocolType) {
   // as histograms can get affected by other tests. In particular,
   // SocketStreamTest and WebSocketTest can affect the histograms.
   scoped_ptr<HistogramSamples> original;
-  Histogram* histogram =
+  HistogramBase* histogram =
       StatisticsRecorder::FindHistogram("Net.SocketStream.ProtocolType");
   if (histogram) {
     original = histogram->SnapshotSamples();
@@ -40,7 +41,7 @@ TEST(SocketStreamMetricsTest, ProtocolType) {
   histogram =
       StatisticsRecorder::FindHistogram("Net.SocketStream.ProtocolType");
   ASSERT_TRUE(histogram != NULL);
-  EXPECT_EQ(Histogram::kUmaTargetedHistogramFlag, histogram->flags());
+  EXPECT_EQ(HistogramBase::kUmaTargetedHistogramFlag, histogram->flags());
 
   scoped_ptr<HistogramSamples> samples(histogram->SnapshotSamples());
   if (original.get()) {
@@ -55,7 +56,7 @@ TEST(SocketStreamMetricsTest, ProtocolType) {
 TEST(SocketStreamMetricsTest, ConnectionType) {
   // First we'll preserve the original values.
   scoped_ptr<HistogramSamples> original;
-  Histogram* histogram =
+  HistogramBase* histogram =
       StatisticsRecorder::FindHistogram("Net.SocketStream.ConnectionType");
   if (histogram) {
     original = histogram->SnapshotSamples();
@@ -75,7 +76,7 @@ TEST(SocketStreamMetricsTest, ConnectionType) {
   histogram =
       StatisticsRecorder::FindHistogram("Net.SocketStream.ConnectionType");
   ASSERT_TRUE(histogram != NULL);
-  EXPECT_EQ(Histogram::kUmaTargetedHistogramFlag, histogram->flags());
+  EXPECT_EQ(HistogramBase::kUmaTargetedHistogramFlag, histogram->flags());
 
   scoped_ptr<HistogramSamples> samples(histogram->SnapshotSamples());
   if (original.get()) {
@@ -90,7 +91,7 @@ TEST(SocketStreamMetricsTest, ConnectionType) {
 TEST(SocketStreamMetricsTest, WireProtocolType) {
   // First we'll preserve the original values.
   scoped_ptr<HistogramSamples> original;
-  Histogram* histogram =
+  HistogramBase* histogram =
       StatisticsRecorder::FindHistogram("Net.SocketStream.WireProtocolType");
   if (histogram) {
     original = histogram->SnapshotSamples();
@@ -106,7 +107,7 @@ TEST(SocketStreamMetricsTest, WireProtocolType) {
   histogram =
       StatisticsRecorder::FindHistogram("Net.SocketStream.WireProtocolType");
   ASSERT_TRUE(histogram != NULL);
-  EXPECT_EQ(Histogram::kUmaTargetedHistogramFlag, histogram->flags());
+  EXPECT_EQ(HistogramBase::kUmaTargetedHistogramFlag, histogram->flags());
 
   scoped_ptr<HistogramSamples> samples(histogram->SnapshotSamples());
   if (original.get()) {
@@ -125,7 +126,7 @@ TEST(SocketStreamMetricsTest, OtherNumbers) {
 
   scoped_ptr<HistogramSamples> original;
 
-  Histogram* histogram =
+  HistogramBase* histogram =
       StatisticsRecorder::FindHistogram("Net.SocketStream.ReceivedBytes");
   if (histogram) {
     original = histogram->SnapshotSamples();
@@ -167,28 +168,28 @@ TEST(SocketStreamMetricsTest, OtherNumbers) {
   histogram =
       StatisticsRecorder::FindHistogram("Net.SocketStream.ConnectionLatency");
   ASSERT_TRUE(histogram != NULL);
-  EXPECT_EQ(Histogram::kUmaTargetedHistogramFlag, histogram->flags());
+  EXPECT_EQ(HistogramBase::kUmaTargetedHistogramFlag, histogram->flags());
   // We don't check the contents of the histogram as it's time sensitive.
 
   // ConnectionEstablish.
   histogram =
       StatisticsRecorder::FindHistogram("Net.SocketStream.ConnectionEstablish");
   ASSERT_TRUE(histogram != NULL);
-  EXPECT_EQ(Histogram::kUmaTargetedHistogramFlag, histogram->flags());
+  EXPECT_EQ(HistogramBase::kUmaTargetedHistogramFlag, histogram->flags());
   // We don't check the contents of the histogram as it's time sensitive.
 
   // Duration.
   histogram =
       StatisticsRecorder::FindHistogram("Net.SocketStream.Duration");
   ASSERT_TRUE(histogram != NULL);
-  EXPECT_EQ(Histogram::kUmaTargetedHistogramFlag, histogram->flags());
+  EXPECT_EQ(HistogramBase::kUmaTargetedHistogramFlag, histogram->flags());
   // We don't check the contents of the histogram as it's time sensitive.
 
   // ReceivedBytes.
   histogram =
       StatisticsRecorder::FindHistogram("Net.SocketStream.ReceivedBytes");
   ASSERT_TRUE(histogram != NULL);
-  EXPECT_EQ(Histogram::kUmaTargetedHistogramFlag, histogram->flags());
+  EXPECT_EQ(HistogramBase::kUmaTargetedHistogramFlag, histogram->flags());
   samples = histogram->SnapshotSamples();
   EXPECT_EQ(11, samples->sum() - original_received_bytes);  // 11 bytes read.
 
@@ -196,7 +197,7 @@ TEST(SocketStreamMetricsTest, OtherNumbers) {
   histogram =
       StatisticsRecorder::FindHistogram("Net.SocketStream.ReceivedCounts");
   ASSERT_TRUE(histogram != NULL);
-  EXPECT_EQ(Histogram::kUmaTargetedHistogramFlag, histogram->flags());
+  EXPECT_EQ(HistogramBase::kUmaTargetedHistogramFlag, histogram->flags());
   samples = histogram->SnapshotSamples();
   EXPECT_EQ(2, samples->sum() - original_received_counts);  // 2 read requests.
 
@@ -204,7 +205,7 @@ TEST(SocketStreamMetricsTest, OtherNumbers) {
   histogram =
       StatisticsRecorder::FindHistogram("Net.SocketStream.SentBytes");
   ASSERT_TRUE(histogram != NULL);
-  EXPECT_EQ(Histogram::kUmaTargetedHistogramFlag, histogram->flags());
+  EXPECT_EQ(HistogramBase::kUmaTargetedHistogramFlag, histogram->flags());
   samples = histogram->SnapshotSamples();
   EXPECT_EQ(222, samples->sum() - original_sent_bytes);  // 222 bytes sent.
 
@@ -212,7 +213,7 @@ TEST(SocketStreamMetricsTest, OtherNumbers) {
   histogram =
       StatisticsRecorder::FindHistogram("Net.SocketStream.SentCounts");
   ASSERT_TRUE(histogram != NULL);
-  EXPECT_EQ(Histogram::kUmaTargetedHistogramFlag, histogram->flags());
+  EXPECT_EQ(HistogramBase::kUmaTargetedHistogramFlag, histogram->flags());
   samples = histogram->SnapshotSamples();
   EXPECT_EQ(3, samples->sum() - original_sent_counts);  // 3 write requests.
 }
diff --git a/net/url_request/url_request_throttler_unittest.cc b/net/url_request/url_request_throttler_unittest.cc
index 998fb06..bb010c3 100644
--- a/net/url_request/url_request_throttler_unittest.cc
+++ b/net/url_request/url_request_throttler_unittest.cc
@@ -29,6 +29,7 @@ namespace net {
 namespace {
 
 using base::Histogram;
+using base::HistogramBase;
 using base::HistogramSamples;
 using base::StatisticsRecorder;
 
@@ -211,7 +212,7 @@ void URLRequestThrottlerEntryTest::SetUp() {
     // Must retrieve original samples for each histogram for comparison
     // as other tests may affect them.
     const char* name = kHistogramNames[i];
-    Histogram* histogram = StatisticsRecorder::FindHistogram(name);
+    HistogramBase* histogram = StatisticsRecorder::FindHistogram(name);
     if (histogram) {
       original_samples_[name] = histogram->SnapshotSamples().release();
     } else {
@@ -230,9 +231,9 @@ void URLRequestThrottlerEntryTest::CalculateHistogramDeltas() {
     const char* name = kHistogramNames[i];
     HistogramSamples* original = original_samples_[name];
 
-    Histogram* histogram = StatisticsRecorder::FindHistogram(name);
+    HistogramBase* histogram = StatisticsRecorder::FindHistogram(name);
     if (histogram) {
-      ASSERT_EQ(Histogram::kUmaTargetedHistogramFlag, histogram->flags());
+      ASSERT_EQ(HistogramBase::kUmaTargetedHistogramFlag, histogram->flags());
 
       scoped_ptr<HistogramSamples> samples(histogram->SnapshotSamples());
       if (original)