Refactor of Histogram related code

base/metrics/histogram.cc

Index: base/metrics/histogram.cc
===================================================================
--- base/metrics/histogram.cc	(revision 148055)
+++ base/metrics/histogram.cc	(working copy)
@@ -20,95 +20,143 @@
 #include "base/stringprintf.h"
 #include "base/synchronization/lock.h"
 
+using std::string;
+using std::vector;
+
 namespace base {
 
-// Static table of checksums for all possible 8 bit bytes.
-const uint32 Histogram::kCrcTable[256] = {0x0, 0x77073096L, 0xee0e612cL,
-0x990951baL, 0x76dc419L, 0x706af48fL, 0xe963a535L, 0x9e6495a3L, 0xedb8832L,
-0x79dcb8a4L, 0xe0d5e91eL, 0x97d2d988L, 0x9b64c2bL, 0x7eb17cbdL, 0xe7b82d07L,
-0x90bf1d91L, 0x1db71064L, 0x6ab020f2L, 0xf3b97148L, 0x84be41deL, 0x1adad47dL,
-0x6ddde4ebL, 0xf4d4b551L, 0x83d385c7L, 0x136c9856L, 0x646ba8c0L, 0xfd62f97aL,
-0x8a65c9ecL, 0x14015c4fL, 0x63066cd9L, 0xfa0f3d63L, 0x8d080df5L, 0x3b6e20c8L,
-0x4c69105eL, 0xd56041e4L, 0xa2677172L, 0x3c03e4d1L, 0x4b04d447L, 0xd20d85fdL,
-0xa50ab56bL, 0x35b5a8faL, 0x42b2986cL, 0xdbbbc9d6L, 0xacbcf940L, 0x32d86ce3L,
-0x45df5c75L, 0xdcd60dcfL, 0xabd13d59L, 0x26d930acL, 0x51de003aL, 0xc8d75180L,
-0xbfd06116L, 0x21b4f4b5L, 0x56b3c423L, 0xcfba9599L, 0xb8bda50fL, 0x2802b89eL,
-0x5f058808L, 0xc60cd9b2L, 0xb10be924L, 0x2f6f7c87L, 0x58684c11L, 0xc1611dabL,
-0xb6662d3dL, 0x76dc4190L, 0x1db7106L, 0x98d220bcL, 0xefd5102aL, 0x71b18589L,
-0x6b6b51fL, 0x9fbfe4a5L, 0xe8b8d433L, 0x7807c9a2L, 0xf00f934L, 0x9609a88eL,
-0xe10e9818L, 0x7f6a0dbbL, 0x86d3d2dL, 0x91646c97L, 0xe6635c01L, 0x6b6b51f4L,
-0x1c6c6162L, 0x856530d8L, 0xf262004eL, 0x6c0695edL, 0x1b01a57bL, 0x8208f4c1L,
-0xf50fc457L, 0x65b0d9c6L, 0x12b7e950L, 0x8bbeb8eaL, 0xfcb9887cL, 0x62dd1ddfL,
-0x15da2d49L, 0x8cd37cf3L, 0xfbd44c65L, 0x4db26158L, 0x3ab551ceL, 0xa3bc0074L,
-0xd4bb30e2L, 0x4adfa541L, 0x3dd895d7L, 0xa4d1c46dL, 0xd3d6f4fbL, 0x4369e96aL,
-0x346ed9fcL, 0xad678846L, 0xda60b8d0L, 0x44042d73L, 0x33031de5L, 0xaa0a4c5fL,
-0xdd0d7cc9L, 0x5005713cL, 0x270241aaL, 0xbe0b1010L, 0xc90c2086L, 0x5768b525L,
-0x206f85b3L, 0xb966d409L, 0xce61e49fL, 0x5edef90eL, 0x29d9c998L, 0xb0d09822L,
-0xc7d7a8b4L, 0x59b33d17L, 0x2eb40d81L, 0xb7bd5c3bL, 0xc0ba6cadL, 0xedb88320L,
-0x9abfb3b6L, 0x3b6e20cL, 0x74b1d29aL, 0xead54739L, 0x9dd277afL, 0x4db2615L,
-0x73dc1683L, 0xe3630b12L, 0x94643b84L, 0xd6d6a3eL, 0x7a6a5aa8L, 0xe40ecf0bL,
-0x9309ff9dL, 0xa00ae27L, 0x7d079eb1L, 0xf00f9344L, 0x8708a3d2L, 0x1e01f268L,
-0x6906c2feL, 0xf762575dL, 0x806567cbL, 0x196c3671L, 0x6e6b06e7L, 0xfed41b76L,
-0x89d32be0L, 0x10da7a5aL, 0x67dd4accL, 0xf9b9df6fL, 0x8ebeeff9L, 0x17b7be43L,
-0x60b08ed5L, 0xd6d6a3e8L, 0xa1d1937eL, 0x38d8c2c4L, 0x4fdff252L, 0xd1bb67f1L,
-0xa6bc5767L, 0x3fb506ddL, 0x48b2364bL, 0xd80d2bdaL, 0xaf0a1b4cL, 0x36034af6L,
-0x41047a60L, 0xdf60efc3L, 0xa867df55L, 0x316e8eefL, 0x4669be79L, 0xcb61b38cL,
-0xbc66831aL, 0x256fd2a0L, 0x5268e236L, 0xcc0c7795L, 0xbb0b4703L, 0x220216b9L,
-0x5505262fL, 0xc5ba3bbeL, 0xb2bd0b28L, 0x2bb45a92L, 0x5cb36a04L, 0xc2d7ffa7L,
-0xb5d0cf31L, 0x2cd99e8bL, 0x5bdeae1dL, 0x9b64c2b0L, 0xec63f226L, 0x756aa39cL,
-0x26d930aL, 0x9c0906a9L, 0xeb0e363fL, 0x72076785L, 0x5005713L, 0x95bf4a82L,
-0xe2b87a14L, 0x7bb12baeL, 0xcb61b38L, 0x92d28e9bL, 0xe5d5be0dL, 0x7cdcefb7L,
-0xbdbdf21L, 0x86d3d2d4L, 0xf1d4e242L, 0x68ddb3f8L, 0x1fda836eL, 0x81be16cdL,
-0xf6b9265bL, 0x6fb077e1L, 0x18b74777L, 0x88085ae6L, 0xff0f6a70L, 0x66063bcaL,
-0x11010b5cL, 0x8f659effL, 0xf862ae69L, 0x616bffd3L, 0x166ccf45L, 0xa00ae278L,
-0xd70dd2eeL, 0x4e048354L, 0x3903b3c2L, 0xa7672661L, 0xd06016f7L, 0x4969474dL,
-0x3e6e77dbL, 0xaed16a4aL, 0xd9d65adcL, 0x40df0b66L, 0x37d83bf0L, 0xa9bcae53L,
-0xdebb9ec5L, 0x47b2cf7fL, 0x30b5ffe9L, 0xbdbdf21cL, 0xcabac28aL, 0x53b39330L,
-0x24b4a3a6L, 0xbad03605L, 0xcdd70693L, 0x54de5729L, 0x23d967bfL, 0xb3667a2eL,
-0xc4614ab8L, 0x5d681b02L, 0x2a6f2b94L, 0xb40bbe37L, 0xc30c8ea1L, 0x5a05df1bL,
-0x2d02ef8dL,
-};
+typedef HistogramBase::Count Count;
+typedef HistogramBase::Sample Sample;
 
-typedef Histogram::Count Count;
-
 // static
 const size_t Histogram::kBucketCount_MAX = 16384u;
 
-Histogram* Histogram::FactoryGet(const std::string& name,
+Histogram::SampleSet::SampleSet(size_t size)
+    : counts_(size, 0),
+      sum_(0),
+      redundant_count_(0) {}
+
+Histogram::SampleSet::SampleSet()
+    : counts_(),
+      sum_(0),
+      redundant_count_(0) {}
+
+Histogram::SampleSet::~SampleSet() {}
+
+void Histogram::SampleSet::Resize(size_t size) {
+  counts_.resize(size, 0);
+}
+
+void Histogram::SampleSet::Accumulate(Sample value,  Count count,
+                                      size_t index) {
+  DCHECK(count == 1 || count == -1);
+  counts_[index] += count;
+  sum_ += count * value;
+  redundant_count_ += count;
+  DCHECK_GE(counts_[index], 0);
+  DCHECK_GE(sum_, 0);
+  DCHECK_GE(redundant_count_, 0);
+}
+
+Count Histogram::SampleSet::TotalCount() const {
+  Count total = 0;
+  for (Counts::const_iterator it = counts_.begin();
+       it != counts_.end();
+       ++it) {
+    total += *it;
+  }
+  return total;
+}
+
+void Histogram::SampleSet::Add(const SampleSet& other) {
+  DCHECK_EQ(counts_.size(), other.counts_.size());
+  sum_ += other.sum_;
+  redundant_count_ += other.redundant_count_;
+  for (size_t index = 0; index < counts_.size(); ++index)
+    counts_[index] += other.counts_[index];
+}
+
+void Histogram::SampleSet::Subtract(const SampleSet& other) {
+  DCHECK_EQ(counts_.size(), other.counts_.size());
+  // Note: Race conditions in snapshotting a sum may lead to (temporary)
+  // negative values when snapshots are later combined (and deltas calculated).
+  // As a result, we don't currently CHCEK() for positive values.
+  sum_ -= other.sum_;
+  redundant_count_ -= other.redundant_count_;
+  for (size_t index = 0; index < counts_.size(); ++index) {
+    counts_[index] -= other.counts_[index];
+    DCHECK_GE(counts_[index], 0);
+  }
+}
+
+bool Histogram::SampleSet::Serialize(Pickle* pickle) const {
+  pickle->WriteInt64(sum_);
+  pickle->WriteInt64(redundant_count_);
+  pickle->WriteUInt64(counts_.size());
+
+  for (size_t index = 0; index < counts_.size(); ++index) {
+    pickle->WriteInt(counts_[index]);
+  }
+
+  return true;
+}
+
+bool Histogram::SampleSet::Deserialize(PickleIterator* iter) {
+  DCHECK_EQ(counts_.size(), 0u);
+  DCHECK_EQ(sum_, 0);
+  DCHECK_EQ(redundant_count_, 0);
+
+  uint64 counts_size;
+
+  if (!iter->ReadInt64(&sum_) ||
+      !iter->ReadInt64(&redundant_count_) ||
+      !iter->ReadUInt64(&counts_size)) {
+    return false;
+  }
+
+  if (counts_size == 0)
+    return false;
+
+  int count = 0;
+  for (uint64 index = 0; index < counts_size; ++index) {
+    int i;
+    if (!iter->ReadInt(&i))
+      return false;
+    counts_.push_back(i);
+    count += i;
+  }
+  DCHECK_EQ(count, redundant_count_);
+  return count == redundant_count_;
+}
+
+Histogram* Histogram::FactoryGet(const string& name,
                                  Sample minimum,
                                  Sample maximum,
                                  size_t bucket_count,
                                  Flags flags) {
-  // Defensive code.
-  if (minimum < 1)
-    minimum = 1;
-  if (maximum > kSampleType_MAX - 1)
-    maximum = kSampleType_MAX - 1;
+  CHECK(InspectConstructionArguments(name, &minimum, &maximum, &bucket_count));
 
-  DCHECK_GT(maximum, minimum);
-  DCHECK_GT((Sample) bucket_count, 2);
-  DCHECK_LE((Sample) bucket_count, maximum - minimum + 2);
-
   Histogram* histogram = StatisticsRecorder::FindHistogram(name);
   if (!histogram) {
-    // Extra variable is not needed... but this keeps this section basically
-    // identical to other derived classes in this file (and compiler will
-    // optimize away the extra variable.
     // To avoid racy destruction at shutdown, the following will be leaked.
+    BucketRanges* ranges = new BucketRanges(bucket_count + 1);
+    InitializeBucketRanges(minimum, maximum, bucket_count, ranges);
+    const BucketRanges* registered_ranges =
+        StatisticsRecorder::RegisterOrDeleteDuplicateRanges(ranges);
+
     Histogram* tentative_histogram =
-        new Histogram(name, minimum, maximum, bucket_count);
-    tentative_histogram->InitializeBucketRange();
+        new Histogram(name, minimum, maximum, bucket_count, registered_ranges);
     tentative_histogram->SetFlags(flags);
     histogram =
         StatisticsRecorder::RegisterOrDeleteDuplicate(tentative_histogram);
   }
 
-  DCHECK_EQ(HISTOGRAM, histogram->histogram_type());
-  DCHECK(histogram->HasConstructorArguments(minimum, maximum, bucket_count));
+  CHECK_EQ(HISTOGRAM, histogram->histogram_type());
+  CHECK(histogram->HasConstructionArguments(minimum, maximum, bucket_count));
   return histogram;
 }
 
-Histogram* Histogram::FactoryTimeGet(const std::string& name,
+Histogram* Histogram::FactoryTimeGet(const string& name,
                                      TimeDelta minimum,
                                      TimeDelta maximum,
                                      size_t bucket_count,
@@ -125,6 +173,47 @@
 #endif
 }
 
+// Calculate what range of values are held in each bucket.
+// We have to be careful that we don't pick a ratio between starting points in
+// consecutive buckets that is sooo small, that the integer bounds are the same
+// (effectively making one bucket get no values).  We need to avoid:
+//   ranges(i) == ranges(i + 1)
+// To avoid that, we just do a fine-grained bucket width as far as we need to
+// until we get a ratio that moves us along at least 2 units at a time.  From
+// that bucket onward we do use the exponential growth of buckets.
+//
+// static
+void Histogram::InitializeBucketRanges(Sample minimum,
+                                       Sample maximum,
+                                       size_t bucket_count,
+                                       BucketRanges* ranges) {
+  DCHECK_EQ(ranges->size(), bucket_count + 1);
+  double log_max = log(static_cast<double>(maximum));
+  double log_ratio;
+  double log_next;
+  size_t bucket_index = 1;
+  Sample current = minimum;
+  ranges->set_range(bucket_index, current);
+  while (bucket_count > ++bucket_index) {
+    double log_current;
+    log_current = log(static_cast<double>(current));
+    // Calculate the count'th root of the range.
+    log_ratio = (log_max - log_current) / (bucket_count - bucket_index);
+    // See where the next bucket would start.
+    log_next = log_current + log_ratio;
+    Sample next;
+    next = static_cast<int>(floor(exp(log_next) + 0.5));
+    if (next > current)
+      current = next;
+    else
+      ++current;  // Just do a narrow bucket, and keep trying.
+    ranges->set_range(bucket_index, current);
+  }
+  ranges->set_range(ranges->size() - 1, HistogramBase::kSampleType_MAX);
+  ranges->ResetChecksum();
+}
+
+// static
 void Histogram::Add(int value) {
   if (value > kSampleType_MAX - 1)
     value = kSampleType_MAX - 1;
@@ -149,93 +238,29 @@
 }
 
 // The following methods provide a graphical histogram display.
-void Histogram::WriteHTMLGraph(std::string* output) const {
+void Histogram::WriteHTMLGraph(string* output) const {
   // TBD(jar) Write a nice HTML bar chart, with divs an mouse-overs etc.
   output->append("<PRE>");
   WriteAsciiImpl(true, "<br>", output);
   output->append("</PRE>");
 }
 
-void Histogram::WriteAscii(std::string* output) const {
+void Histogram::WriteAscii(string* output) const {
   WriteAsciiImpl(true, "\n", output);
 }
 
-void Histogram::WriteAsciiImpl(bool graph_it,
-                               const std::string& newline,
-                               std::string* output) const {
-  // Get local (stack) copies of all effectively volatile class data so that we
-  // are consistent across our output activities.
-  SampleSet snapshot;
-  SnapshotSample(&snapshot);
-  Count sample_count = snapshot.TotalCount();
-
-  WriteAsciiHeader(snapshot, sample_count, output);
-  output->append(newline);
-
-  // Prepare to normalize graphical rendering of bucket contents.
-  double max_size = 0;
-  if (graph_it)
-    max_size = GetPeakBucketSize(snapshot);
-
-  // Calculate space needed to print bucket range numbers.  Leave room to print
-  // nearly the largest bucket range without sliding over the histogram.
-  size_t largest_non_empty_bucket = bucket_count() - 1;
-  while (0 == snapshot.counts(largest_non_empty_bucket)) {
-    if (0 == largest_non_empty_bucket)
-      break;  // All buckets are empty.
-    --largest_non_empty_bucket;
-  }
-
-  // Calculate largest print width needed for any of our bucket range displays.
-  size_t print_width = 1;
-  for (size_t i = 0; i < bucket_count(); ++i) {
-    if (snapshot.counts(i)) {
-      size_t width = GetAsciiBucketRange(i).size() + 1;
-      if (width > print_width)
-        print_width = width;
-    }
-  }
-
-  int64 remaining = sample_count;
-  int64 past = 0;
-  // Output the actual histogram graph.
-  for (size_t i = 0; i < bucket_count(); ++i) {
-    Count current = snapshot.counts(i);
-    if (!current && !PrintEmptyBucket(i))
-      continue;
-    remaining -= current;
-    std::string range = GetAsciiBucketRange(i);
-    output->append(range);
-    for (size_t j = 0; range.size() + j < print_width + 1; ++j)
-      output->push_back(' ');
-    if (0 == current && i < bucket_count() - 1 && 0 == snapshot.counts(i + 1)) {
-      while (i < bucket_count() - 1 && 0 == snapshot.counts(i + 1))
-        ++i;
-      output->append("... ");
-      output->append(newline);
-      continue;  // No reason to plot emptiness.
-    }
-    double current_size = GetBucketSize(current, i);
-    if (graph_it)
-      WriteAsciiBucketGraph(current_size, max_size, output);
-    WriteAsciiBucketContext(past, current, remaining, i, output);
-    output->append(newline);
-    past += current;
-  }
-  DCHECK_EQ(sample_count, past);
-}
-
 // static
-std::string Histogram::SerializeHistogramInfo(const Histogram& histogram,
-                                              const SampleSet& snapshot) {
+string Histogram::SerializeHistogramInfo(const Histogram& histogram,
+                                         const SampleSet& snapshot) {
   DCHECK_NE(NOT_VALID_IN_RENDERER, histogram.histogram_type());
+  DCHECK(histogram.bucket_ranges()->HasValidChecksum());
 
   Pickle pickle;
   pickle.WriteString(histogram.histogram_name());
   pickle.WriteInt(histogram.declared_min());
   pickle.WriteInt(histogram.declared_max());
   pickle.WriteUInt64(histogram.bucket_count());
-  pickle.WriteUInt32(histogram.range_checksum());
+  pickle.WriteUInt32(histogram.bucket_ranges()->checksum());
   pickle.WriteInt(histogram.histogram_type());
   pickle.WriteInt(histogram.flags());
 
@@ -243,18 +268,18 @@
 
   histogram.SerializeRanges(&pickle);
 
-  return std::string(static_cast<const char*>(pickle.data()), pickle.size());
+  return string(static_cast<const char*>(pickle.data()), pickle.size());
 }
 
 // static
-bool Histogram::DeserializeHistogramInfo(const std::string& histogram_info) {
+bool Histogram::DeserializeHistogramInfo(const string& histogram_info) {
   if (histogram_info.empty()) {
     return false;
   }
 
   Pickle pickle(histogram_info.data(),
                 static_cast<int>(histogram_info.size()));
-  std::string histogram_name;
+  string histogram_name;
   int declared_min;
   int declared_max;
   uint64 bucket_count;
@@ -300,7 +325,7 @@
   } else if (histogram_type == BOOLEAN_HISTOGRAM) {
     render_histogram = BooleanHistogram::FactoryGet(histogram_name, flags);
   } else if (histogram_type == CUSTOM_HISTOGRAM) {
-    std::vector<Histogram::Sample> sample_ranges(bucket_count);
+    vector<Sample> sample_ranges(bucket_count);
     if (!CustomHistogram::DeserializeRanges(&iter, &sample_ranges)) {
       DLOG(ERROR) << "Pickle error decoding ranges: " << histogram_name;
       return false;
@@ -316,9 +341,12 @@
   DCHECK_EQ(render_histogram->declared_min(), declared_min);
   DCHECK_EQ(render_histogram->declared_max(), declared_max);
   DCHECK_EQ(render_histogram->bucket_count(), bucket_count);
-  DCHECK_EQ(render_histogram->range_checksum(), range_checksum);
   DCHECK_EQ(render_histogram->histogram_type(), histogram_type);
 
+  if (render_histogram->bucket_ranges()->checksum() != range_checksum) {
+    return false;
+  }
+
   if (render_histogram->flags() & kIPCSerializationSourceFlag) {
     DVLOG(1) << "Single process mode, histogram observed and not copied: "
              << histogram_name;
@@ -330,10 +358,8 @@
   return true;
 }
 
-//------------------------------------------------------------------------------
-// Methods for the validating a sample and a related histogram.
-//------------------------------------------------------------------------------
 
+// Validate a sample and related histogram.
 Histogram::Inconsistencies Histogram::FindCorruption(
     const SampleSet& snapshot) const {
   int inconsistencies = NO_INCONSISTENCIES;
@@ -347,7 +373,7 @@
     previous_range = new_range;
   }
 
-  if (!HasValidRangeChecksum())
+  if (!bucket_ranges()->HasValidChecksum())
     inconsistencies |= RANGE_CHECKSUM_ERROR;
 
   int64 delta64 = snapshot.redundant_count() - count;
@@ -382,7 +408,7 @@
   return HISTOGRAM;
 }
 
-Histogram::Sample Histogram::ranges(size_t i) const {
+Sample Histogram::ranges(size_t i) const {
   return bucket_ranges_->range(i);
 }
 
@@ -397,101 +423,60 @@
   *sample = sample_;
 }
 
-bool Histogram::HasConstructorArguments(Sample minimum,
-                                        Sample maximum,
-                                        size_t bucket_count) {
+bool Histogram::HasConstructionArguments(Sample minimum,
+                                         Sample maximum,
+                                         size_t bucket_count) {
   return ((minimum == declared_min_) && (maximum == declared_max_) &&
           (bucket_count == bucket_count_));
 }
 
-bool Histogram::HasConstructorTimeDeltaArguments(TimeDelta minimum,
-                                                 TimeDelta maximum,
-                                                 size_t bucket_count) {
-  return ((minimum.InMilliseconds() == declared_min_) &&
-          (maximum.InMilliseconds() == declared_max_) &&
-          (bucket_count == bucket_count_));
-}
-
-bool Histogram::HasValidRangeChecksum() const {
-  return CalculateRangeChecksum() == range_checksum_;
-}
-
-Histogram::Histogram(const std::string& name, Sample minimum,
-                     Sample maximum, size_t bucket_count)
+Histogram::Histogram(const string& name,
+                     Sample minimum,
+                     Sample maximum,
+                     size_t bucket_count,
+                     const BucketRanges* ranges)
   : HistogramBase(name),
+    bucket_ranges_(ranges),
     declared_min_(minimum),
     declared_max_(maximum),
     bucket_count_(bucket_count),
     flags_(kNoFlags),
-    bucket_ranges_(new BucketRanges(bucket_count + 1)),
-    range_checksum_(0),
-    sample_() {
-  Initialize();
-}
+    sample_(bucket_count) {}
 
-Histogram::Histogram(const std::string& name, TimeDelta minimum,
-                     TimeDelta maximum, size_t bucket_count)
-  : HistogramBase(name),
-    declared_min_(static_cast<int> (minimum.InMilliseconds())),
-    declared_max_(static_cast<int> (maximum.InMilliseconds())),
-    bucket_count_(bucket_count),
-    flags_(kNoFlags),
-    bucket_ranges_(new BucketRanges(bucket_count + 1)),
-    range_checksum_(0),
-    sample_() {
-  Initialize();
-}
-
 Histogram::~Histogram() {
   if (StatisticsRecorder::dump_on_exit()) {
-    std::string output;
+    string output;
     WriteAsciiImpl(true, "\n", &output);
     DLOG(INFO) << output;
   }
+}
 
-  // Just to make sure most derived class did this properly...
-  DCHECK(ValidateBucketRanges());
+// static
+bool Histogram::InspectConstructionArguments(const string& name,
+                                             Sample* minimum,
+                                             Sample* maximum,
+                                             size_t* bucket_count) {
+  // Defensive code for backward compatibility.
+  if (*minimum < 1) {
+    DLOG(WARNING) << "Histogram: " << name << " Bad minimum: " << *minimum;
+    *minimum = 1;
+  }
+  if (*maximum >= kSampleType_MAX) {
+    DLOG(WARNING) << "Histogram: " << name << " Bad maximum: " << *maximum;
+    *maximum = kSampleType_MAX;
+  }
+
+  if (*bucket_count < 3 || *bucket_count >= kBucketCount_MAX)
+    return false;
+  if (*bucket_count > static_cast<size_t>(*maximum - *minimum + 2))
+    return false;
+  return true;
 }
 
 bool Histogram::SerializeRanges(Pickle* pickle) const {
   return true;
 }
 
-// Calculate what range of values are held in each bucket.
-// We have to be careful that we don't pick a ratio between starting points in
-// consecutive buckets that is sooo small, that the integer bounds are the same
-// (effectively making one bucket get no values).  We need to avoid:
-//   ranges(i) == ranges(i + 1)
-// To avoid that, we just do a fine-grained bucket width as far as we need to
-// until we get a ratio that moves us along at least 2 units at a time.  From
-// that bucket onward we do use the exponential growth of buckets.
-void Histogram::InitializeBucketRange() {
-  double log_max = log(static_cast<double>(declared_max()));
-  double log_ratio;
-  double log_next;
-  size_t bucket_index = 1;
-  Sample current = declared_min();
-  SetBucketRange(bucket_index, current);
-  while (bucket_count() > ++bucket_index) {
-    double log_current;
-    log_current = log(static_cast<double>(current));
-    // Calculate the count'th root of the range.
-    log_ratio = (log_max - log_current) / (bucket_count() - bucket_index);
-    // See where the next bucket would start.
-    log_next = log_current + log_ratio;
-    int next;
-    next = static_cast<int>(floor(exp(log_next) + 0.5));
-    if (next > current)
-      current = next;
-    else
-      ++current;  // Just do a narrow bucket, and keep trying.
-    SetBucketRange(bucket_index, current);
-  }
-  ResetRangeChecksum();
-
-  DCHECK_EQ(bucket_count(), bucket_index);
-}
-
 bool Histogram::PrintEmptyBucket(size_t index) const {
   return true;
 }
@@ -535,12 +520,8 @@
   return current/denominator;
 }
 
-void Histogram::ResetRangeChecksum() {
-  range_checksum_ = CalculateRangeChecksum();
-}
-
-const std::string Histogram::GetAsciiBucketRange(size_t i) const {
-  std::string result;
+const string Histogram::GetAsciiBucketRange(size_t i) const {
+  string result;
   if (kHexRangePrintingFlag & flags_)
     StringAppendF(&result, "%#x", ranges(i));
   else
@@ -554,85 +535,74 @@
   sample_.Accumulate(value, count, index);
 }
 
-void Histogram::SetBucketRange(size_t i, Sample value) {
-  DCHECK_GT(bucket_count_, i);
-  DCHECK_GE(value, 0);
-  bucket_ranges_->set_range(i, value);
-}
+//------------------------------------------------------------------------------
+// Private methods
 
-bool Histogram::ValidateBucketRanges() const {
-  // Standard assertions that all bucket ranges should satisfy.
-  DCHECK_EQ(bucket_count_ + 1, bucket_ranges_->size());
-  DCHECK_EQ(0, ranges(0));
-  DCHECK_EQ(declared_min(), ranges(1));
-  DCHECK_EQ(declared_max(), ranges(bucket_count_ - 1));
-  DCHECK_EQ(kSampleType_MAX, ranges(bucket_count_));
-  return true;
-}
+void Histogram::WriteAsciiImpl(bool graph_it,
+                               const string& newline,
+                               string* output) const {
+  // Get local (stack) copies of all effectively volatile class data so that we
+  // are consistent across our output activities.
+  SampleSet snapshot;
+  SnapshotSample(&snapshot);
+  Count sample_count = snapshot.TotalCount();
 
-uint32 Histogram::CalculateRangeChecksum() const {
-  DCHECK_EQ(bucket_ranges_->size(), bucket_count() + 1);
-  // Seed checksum.
-  uint32 checksum = static_cast<uint32>(bucket_ranges_->size());
-  for (size_t index = 0; index < bucket_count(); ++index)
-    checksum = Crc32(checksum, ranges(index));
-  return checksum;
-}
+  WriteAsciiHeader(snapshot, sample_count, output);
+  output->append(newline);
 
-void Histogram::Initialize() {
-  sample_.Resize(*this);
-  if (declared_min_ < 1)
-    declared_min_ = 1;
-  if (declared_max_ > kSampleType_MAX - 1)
-    declared_max_ = kSampleType_MAX - 1;
-  DCHECK_LE(declared_min_, declared_max_);
-  DCHECK_GT(bucket_count_, 1u);
-  CHECK_LT(bucket_count_, kBucketCount_MAX);
-  size_t maximal_bucket_count = declared_max_ - declared_min_ + 2;
-  DCHECK_LE(bucket_count_, maximal_bucket_count);
-  DCHECK_EQ(0, ranges(0));
-  bucket_ranges_->set_range(bucket_count_, kSampleType_MAX);
-}
+  // Prepare to normalize graphical rendering of bucket contents.
+  double max_size = 0;
+  if (graph_it)
+    max_size = GetPeakBucketSize(snapshot);
 
-// We generate the CRC-32 using the low order bits to select whether to XOR in
-// the reversed polynomial 0xedb88320L.  This is nice and simple, and allows us
-// to keep the quotient in a uint32.  Since we're not concerned about the nature
-// of corruptions (i.e., we don't care about bit sequencing, since we are
-// handling memory changes, which are more grotesque) so we don't bother to
-// get the CRC correct for big-endian vs little-ending calculations.  All we
-// need is a nice hash, that tends to depend on all the bits of the sample, with
-// very little chance of changes in one place impacting changes in another
-// place.
-uint32 Histogram::Crc32(uint32 sum, Histogram::Sample range) {
-  const bool kUseRealCrc = true;  // TODO(jar): Switch to false and watch stats.
-  if (kUseRealCrc) {
-    union {
-      Histogram::Sample range;
-      unsigned char bytes[sizeof(Histogram::Sample)];
-    } converter;
-    converter.range = range;
-    for (size_t i = 0; i < sizeof(converter); ++i)
-      sum = kCrcTable[(sum & 0xff) ^ converter.bytes[i]] ^ (sum >> 8);
-  } else {
-    // Use hash techniques provided in ReallyFastHash, except we don't care
-    // about "avalanching" (which would worsten the hash, and add collisions),
-    // and we don't care about edge cases since we have an even number of bytes.
-    union {
-      Histogram::Sample range;
-      uint16 ints[sizeof(Histogram::Sample) / 2];
-    } converter;
-    DCHECK_EQ(sizeof(Histogram::Sample), sizeof(converter));
-    converter.range = range;
-    sum += converter.ints[0];
-    sum = (sum << 16) ^ sum ^ (static_cast<uint32>(converter.ints[1]) << 11);
-    sum += sum >> 11;
+  // Calculate space needed to print bucket range numbers.  Leave room to print
+  // nearly the largest bucket range without sliding over the histogram.
+  size_t largest_non_empty_bucket = bucket_count() - 1;
+  while (0 == snapshot.counts(largest_non_empty_bucket)) {
+    if (0 == largest_non_empty_bucket)
+      break;  // All buckets are empty.
+    --largest_non_empty_bucket;
   }
-  return sum;
-}
 
-//------------------------------------------------------------------------------
-// Private methods
+  // Calculate largest print width needed for any of our bucket range displays.
+  size_t print_width = 1;
+  for (size_t i = 0; i < bucket_count(); ++i) {
+    if (snapshot.counts(i)) {
+      size_t width = GetAsciiBucketRange(i).size() + 1;
+      if (width > print_width)
+        print_width = width;
+    }
+  }
 
+  int64 remaining = sample_count;
+  int64 past = 0;
+  // Output the actual histogram graph.
+  for (size_t i = 0; i < bucket_count(); ++i) {
+    Count current = snapshot.counts(i);
+    if (!current && !PrintEmptyBucket(i))
+      continue;
+    remaining -= current;
+    string range = GetAsciiBucketRange(i);
+    output->append(range);
+    for (size_t j = 0; range.size() + j < print_width + 1; ++j)
+      output->push_back(' ');
+    if (0 == current && i < bucket_count() - 1 && 0 == snapshot.counts(i + 1)) {
+      while (i < bucket_count() - 1 && 0 == snapshot.counts(i + 1))
+        ++i;
+      output->append("... ");
+      output->append(newline);
+      continue;  // No reason to plot emptiness.
+    }
+    double current_size = GetBucketSize(current, i);
+    if (graph_it)
+      WriteAsciiBucketGraph(current_size, max_size, output);
+    WriteAsciiBucketContext(past, current, remaining, i, output);
+    output->append(newline);
+    past += current;
+  }
+  DCHECK_EQ(sample_count, past);
+}
+
 double Histogram::GetPeakBucketSize(const SampleSet& snapshot) const {
   double max = 0;
   for (size_t i = 0; i < bucket_count() ; ++i) {
@@ -645,7 +615,7 @@
 
 void Histogram::WriteAsciiHeader(const SampleSet& snapshot,
                                  Count sample_count,
-                                 std::string* output) const {
+                                 string* output) const {
   StringAppendF(output,
                 "Histogram: %s recorded %d samples",
                 histogram_name().c_str(),
@@ -665,7 +635,7 @@
                                         const Count current,
                                         const int64 remaining,
                                         const size_t i,
-                                        std::string* output) const {
+                                        string* output) const {
   double scaled_sum = (past + current + remaining) / 100.0;
   WriteAsciiBucketValue(current, scaled_sum, output);
   if (0 < i) {
@@ -674,13 +644,15 @@
   }
 }
 
-void Histogram::WriteAsciiBucketValue(Count current, double scaled_sum,
-                                      std::string* output) const {
+void Histogram::WriteAsciiBucketValue(Count current,
+                                      double scaled_sum,
+                                      string* output) const {
   StringAppendF(output, " (%d = %3.1f%%)", current, current/scaled_sum);
 }
 
-void Histogram::WriteAsciiBucketGraph(double current_size, double max_size,
-                                      std::string* output) const {
+void Histogram::WriteAsciiBucketGraph(double current_size,
+                                      double max_size,
+                                      string* output) const {
   const int k_line_length = 72;  // Maximal horizontal width of graph.
   int x_count = static_cast<int>(k_line_length * (current_size / max_size)
                                  + 0.5);
@@ -694,148 +666,42 @@
 }
 
 //------------------------------------------------------------------------------
-// Methods for the Histogram::SampleSet class
-//------------------------------------------------------------------------------
-
-Histogram::SampleSet::SampleSet()
-    : counts_(),
-      sum_(0),
-      redundant_count_(0) {
-}
-
-Histogram::SampleSet::~SampleSet() {
-}
-
-void Histogram::SampleSet::Resize(const Histogram& histogram) {
-  counts_.resize(histogram.bucket_count(), 0);
-}
-
-void Histogram::SampleSet::CheckSize(const Histogram& histogram) const {
-  DCHECK_EQ(histogram.bucket_count(), counts_.size());
-}
-
-
-void Histogram::SampleSet::Accumulate(Sample value,  Count count,
-                                      size_t index) {
-  DCHECK(count == 1 || count == -1);
-  counts_[index] += count;
-  sum_ += count * value;
-  redundant_count_ += count;
-  DCHECK_GE(counts_[index], 0);
-  DCHECK_GE(sum_, 0);
-  DCHECK_GE(redundant_count_, 0);
-}
-
-Count Histogram::SampleSet::TotalCount() const {
-  Count total = 0;
-  for (Counts::const_iterator it = counts_.begin();
-       it != counts_.end();
-       ++it) {
-    total += *it;
-  }
-  return total;
-}
-
-void Histogram::SampleSet::Add(const SampleSet& other) {
-  DCHECK_EQ(counts_.size(), other.counts_.size());
-  sum_ += other.sum_;
-  redundant_count_ += other.redundant_count_;
-  for (size_t index = 0; index < counts_.size(); ++index)
-    counts_[index] += other.counts_[index];
-}
-
-void Histogram::SampleSet::Subtract(const SampleSet& other) {
-  DCHECK_EQ(counts_.size(), other.counts_.size());
-  // Note: Race conditions in snapshotting a sum may lead to (temporary)
-  // negative values when snapshots are later combined (and deltas calculated).
-  // As a result, we don't currently CHCEK() for positive values.
-  sum_ -= other.sum_;
-  redundant_count_ -= other.redundant_count_;
-  for (size_t index = 0; index < counts_.size(); ++index) {
-    counts_[index] -= other.counts_[index];
-    DCHECK_GE(counts_[index], 0);
-  }
-}
-
-bool Histogram::SampleSet::Serialize(Pickle* pickle) const {
-  pickle->WriteInt64(sum_);
-  pickle->WriteInt64(redundant_count_);
-  pickle->WriteUInt64(counts_.size());
-
-  for (size_t index = 0; index < counts_.size(); ++index) {
-    pickle->WriteInt(counts_[index]);
-  }
-
-  return true;
-}
-
-bool Histogram::SampleSet::Deserialize(PickleIterator* iter) {
-  DCHECK_EQ(counts_.size(), 0u);
-  DCHECK_EQ(sum_, 0);
-  DCHECK_EQ(redundant_count_, 0);
-
-  uint64 counts_size;
-
-  if (!iter->ReadInt64(&sum_) ||
-      !iter->ReadInt64(&redundant_count_) ||
-      !iter->ReadUInt64(&counts_size)) {
-    return false;
-  }
-
-  if (counts_size == 0)
-    return false;
-
-  int count = 0;
-  for (uint64 index = 0; index < counts_size; ++index) {
-    int i;
-    if (!iter->ReadInt(&i))
-      return false;
-    counts_.push_back(i);
-    count += i;
-  }
-  DCHECK_EQ(count, redundant_count_);
-  return count == redundant_count_;
-}
-
-//------------------------------------------------------------------------------
 // LinearHistogram: This histogram uses a traditional set of evenly spaced
 // buckets.
 //------------------------------------------------------------------------------
 
-LinearHistogram::~LinearHistogram() {
-}
+LinearHistogram::~LinearHistogram() {}
 
-Histogram* LinearHistogram::FactoryGet(const std::string& name,
+Histogram* LinearHistogram::FactoryGet(const string& name,
                                        Sample minimum,
                                        Sample maximum,
                                        size_t bucket_count,
                                        Flags flags) {
-  if (minimum < 1)
-    minimum = 1;
-  if (maximum > kSampleType_MAX - 1)
-    maximum = kSampleType_MAX - 1;
+  CHECK(Histogram::InspectConstructionArguments(name, &minimum, &maximum,
+                                                &bucket_count));
 
-  DCHECK_GT(maximum, minimum);
-  DCHECK_GT((Sample) bucket_count, 2);
-  DCHECK_LE((Sample) bucket_count, maximum - minimum + 2);
-
   Histogram* histogram = StatisticsRecorder::FindHistogram(name);
   if (!histogram) {
     // To avoid racy destruction at shutdown, the following will be leaked.
+    BucketRanges* ranges = new BucketRanges(bucket_count + 1);
+    InitializeBucketRanges(minimum, maximum, bucket_count, ranges);
+    const BucketRanges* registered_ranges =
+        StatisticsRecorder::RegisterOrDeleteDuplicateRanges(ranges);
+
     LinearHistogram* tentative_histogram =
-        new LinearHistogram(name, minimum, maximum, bucket_count);
-    tentative_histogram->InitializeBucketRange();
+        new LinearHistogram(name, minimum, maximum, bucket_count,
+                            registered_ranges);
     tentative_histogram->SetFlags(flags);
     histogram =
         StatisticsRecorder::RegisterOrDeleteDuplicate(tentative_histogram);
   }
 
-  DCHECK_EQ(LINEAR_HISTOGRAM, histogram->histogram_type());
-  DCHECK(histogram->HasConstructorArguments(minimum, maximum, bucket_count));
+  CHECK_EQ(LINEAR_HISTOGRAM, histogram->histogram_type());
+  CHECK(histogram->HasConstructionArguments(minimum, maximum, bucket_count));
   return histogram;
 }
 
-Histogram* LinearHistogram::FactoryTimeGet(const std::string& name,
+Histogram* LinearHistogram::FactoryTimeGet(const string& name,
                                            TimeDelta minimum,
                                            TimeDelta maximum,
                                            size_t bucket_count,
@@ -855,35 +721,14 @@
   }
 }
 
-LinearHistogram::LinearHistogram(const std::string& name,
+LinearHistogram::LinearHistogram(const string& name,
                                  Sample minimum,
                                  Sample maximum,
-                                 size_t bucket_count)
-    : Histogram(name, minimum >= 1 ? minimum : 1, maximum, bucket_count) {
+                                 size_t bucket_count,
+                                 const BucketRanges* ranges)
+    : Histogram(name, minimum, maximum, bucket_count, ranges) {
 }
 
-LinearHistogram::LinearHistogram(const std::string& name,
-                                 TimeDelta minimum,
-                                 TimeDelta maximum,
-                                 size_t bucket_count)
-    : Histogram(name, minimum >= TimeDelta::FromMilliseconds(1) ?
-                                 minimum : TimeDelta::FromMilliseconds(1),
-                maximum, bucket_count) {
-}
-
-void LinearHistogram::InitializeBucketRange() {
-  DCHECK_GT(declared_min(), 0);  // 0 is the underflow bucket here.
-  double min = declared_min();
-  double max = declared_max();
-  size_t i;
-  for (i = 1; i < bucket_count(); ++i) {
-    double linear_range = (min * (bucket_count() -1 - i) + max * (i - 1)) /
-                          (bucket_count() - 2);
-    SetBucketRange(i, static_cast<int> (linear_range + 0.5));
-  }
-  ResetRangeChecksum();
-}
-
 double LinearHistogram::GetBucketSize(Count current, size_t i) const {
   DCHECK_GT(ranges(i + 1), ranges(i));
   // Adjacent buckets with different widths would have "surprisingly" many (few)
@@ -892,7 +737,7 @@
   return current/denominator;
 }
 
-const std::string LinearHistogram::GetAsciiBucketRange(size_t i) const {
+const string LinearHistogram::GetAsciiBucketRange(size_t i) const {
   int range = ranges(i);
   BucketDescriptionMap::const_iterator it = bucket_description_.find(range);
   if (it == bucket_description_.end())
@@ -904,23 +749,45 @@
   return bucket_description_.find(ranges(index)) == bucket_description_.end();
 }
 
+// static
+void LinearHistogram::InitializeBucketRanges(Sample minimum,
+                                             Sample maximum,
+                                             size_t bucket_count,
+                                             BucketRanges* ranges) {
+  DCHECK_EQ(ranges->size(), bucket_count + 1);
+  double min = minimum;
+  double max = maximum;
+  size_t i;
+  for (i = 1; i < bucket_count; ++i) {
+    double linear_range =
+        (min * (bucket_count -1 - i) + max * (i - 1)) / (bucket_count - 2);
+    ranges->set_range(i, static_cast<Sample>(linear_range + 0.5));
+  }
+  ranges->set_range(ranges->size() - 1, HistogramBase::kSampleType_MAX);
+  ranges->ResetChecksum();
+}
 
 //------------------------------------------------------------------------------
 // This section provides implementation for BooleanHistogram.
 //------------------------------------------------------------------------------
 
-Histogram* BooleanHistogram::FactoryGet(const std::string& name, Flags flags) {
+Histogram* BooleanHistogram::FactoryGet(const string& name, Flags flags) {
   Histogram* histogram = StatisticsRecorder::FindHistogram(name);
   if (!histogram) {
     // To avoid racy destruction at shutdown, the following will be leaked.
-    BooleanHistogram* tentative_histogram = new BooleanHistogram(name);
-    tentative_histogram->InitializeBucketRange();
+    BucketRanges* ranges = new BucketRanges(4);
+    LinearHistogram::InitializeBucketRanges(1, 2, 3, ranges);
+    const BucketRanges* registered_ranges =
+        StatisticsRecorder::RegisterOrDeleteDuplicateRanges(ranges);
+
+    BooleanHistogram* tentative_histogram =
+        new BooleanHistogram(name, registered_ranges);
     tentative_histogram->SetFlags(flags);
     histogram =
         StatisticsRecorder::RegisterOrDeleteDuplicate(tentative_histogram);
   }
 
-  DCHECK_EQ(BOOLEAN_HISTOGRAM, histogram->histogram_type());
+  CHECK_EQ(BOOLEAN_HISTOGRAM, histogram->histogram_type());
   return histogram;
 }
 
@@ -932,43 +799,35 @@
   Add(value ? 1 : 0);
 }
 
-BooleanHistogram::BooleanHistogram(const std::string& name)
-    : LinearHistogram(name, 1, 2, 3) {
-}
+BooleanHistogram::BooleanHistogram(const string& name,
+                                   const BucketRanges* ranges)
+    : LinearHistogram(name, 1, 2, 3, ranges) {}
 
 //------------------------------------------------------------------------------
 // CustomHistogram:
 //------------------------------------------------------------------------------
 
-Histogram* CustomHistogram::FactoryGet(const std::string& name,
-                                       const std::vector<Sample>& custom_ranges,
+Histogram* CustomHistogram::FactoryGet(const string& name,
+                                       const vector<Sample>& custom_ranges,
                                        Flags flags) {
-  // Remove the duplicates in the custom ranges array.
-  std::vector<int> ranges = custom_ranges;
-  ranges.push_back(0);  // Ensure we have a zero value.
-  std::sort(ranges.begin(), ranges.end());
-  ranges.erase(std::unique(ranges.begin(), ranges.end()), ranges.end());
-  if (ranges.size() <= 1) {
-    DCHECK(false);
-    // Note that we pushed a 0 in above, so for defensive code....
-    ranges.push_back(1);  // Put in some data so we can index to [1].
-  }
+  CHECK(ValidateCustomRanges(custom_ranges));
 
-  DCHECK_LT(ranges.back(), kSampleType_MAX);
-
   Histogram* histogram = StatisticsRecorder::FindHistogram(name);
   if (!histogram) {
+    BucketRanges* ranges = CreateBucketRangesFromCustomRanges(custom_ranges);
+    const BucketRanges* registered_ranges =
+        StatisticsRecorder::RegisterOrDeleteDuplicateRanges(ranges);
+
     // To avoid racy destruction at shutdown, the following will be leaked.
-    CustomHistogram* tentative_histogram = new CustomHistogram(name, ranges);
-    tentative_histogram->InitializedCustomBucketRange(ranges);
+    CustomHistogram* tentative_histogram =
+        new CustomHistogram(name, registered_ranges);
     tentative_histogram->SetFlags(flags);
+
     histogram =
         StatisticsRecorder::RegisterOrDeleteDuplicate(tentative_histogram);
   }
 
-  DCHECK_EQ(histogram->histogram_type(), CUSTOM_HISTOGRAM);
-  DCHECK(histogram->HasConstructorArguments(ranges[1], ranges.back(),
-                                            ranges.size()));
+  CHECK_EQ(histogram->histogram_type(), CUSTOM_HISTOGRAM);
   return histogram;
 }
 
@@ -977,9 +836,9 @@
 }
 
 // static
-std::vector<Histogram::Sample> CustomHistogram::ArrayToCustomRanges(
+vector<Sample> CustomHistogram::ArrayToCustomRanges(
     const Sample* values, size_t num_values) {
-  std::vector<Sample> all_values;
+  vector<Sample> all_values;
   for (size_t i = 0; i < num_values; ++i) {
     Sample value = values[i];
     all_values.push_back(value);
@@ -991,13 +850,13 @@
   return all_values;
 }
 
-CustomHistogram::CustomHistogram(const std::string& name,
-                                 const std::vector<Sample>& custom_ranges)
-    : Histogram(name, custom_ranges[1], custom_ranges.back(),
-                custom_ranges.size()) {
-  DCHECK_GT(custom_ranges.size(), 1u);
-  DCHECK_EQ(custom_ranges[0], 0);
-}
+CustomHistogram::CustomHistogram(const string& name,
+                                 const BucketRanges* ranges)
+    : Histogram(name,
+                ranges->range(1),
+                ranges->range(ranges->size() - 2),
+                ranges->size() - 1,
+                ranges) {}
 
 bool CustomHistogram::SerializeRanges(Pickle* pickle) const {
   for (size_t i = 0; i < bucket_ranges()->size(); ++i) {
@@ -1009,7 +868,7 @@
 
 // static
 bool CustomHistogram::DeserializeRanges(
-    PickleIterator* iter, std::vector<Histogram::Sample>* ranges) {
+    PickleIterator* iter, vector<Sample>* ranges) {
   for (size_t i = 0; i < ranges->size(); ++i) {
     if (!iter->ReadInt(&(*ranges)[i]))
       return false;
@@ -1017,18 +876,39 @@
   return true;
 }
 
-void CustomHistogram::InitializedCustomBucketRange(
-    const std::vector<Sample>& custom_ranges) {
-  DCHECK_GT(custom_ranges.size(), 1u);
-  DCHECK_EQ(custom_ranges[0], 0);
-  DCHECK_LE(custom_ranges.size(), bucket_count());
-  for (size_t index = 0; index < custom_ranges.size(); ++index)
-    SetBucketRange(index, custom_ranges[index]);
-  ResetRangeChecksum();
-}
-
 double CustomHistogram::GetBucketSize(Count current, size_t i) const {
   return 1;
 }
 
+// static
+bool CustomHistogram::ValidateCustomRanges(
+    const vector<Sample>& custom_ranges) {
+  if (custom_ranges.size() < 1)
+    return false;
+  for (size_t i = 0; i < custom_ranges.size(); i++) {
+    Sample s = custom_ranges[i];
+    if (s < 0 || s > HistogramBase::kSampleType_MAX - 1)
+      return false;
+  }
+  return true;
+}
+
+// static
+BucketRanges* CustomHistogram::CreateBucketRangesFromCustomRanges(
+      const vector<Sample>& custom_ranges) {
+  // Remove the duplicates in the custom ranges array.
+  vector<int> ranges = custom_ranges;
+  ranges.push_back(0);  // Ensure we have a zero value.
+  ranges.push_back(HistogramBase::kSampleType_MAX);
+  std::sort(ranges.begin(), ranges.end());
+  ranges.erase(std::unique(ranges.begin(), ranges.end()), ranges.end());
+
+  BucketRanges* bucket_ranges = new BucketRanges(ranges.size());
+  for (size_t i = 0; i < ranges.size(); i++) {
+    bucket_ranges->set_range(i, ranges[i]);
+  }
+  bucket_ranges->ResetChecksum();
+  return bucket_ranges;
+}
+
 }  // namespace base