[UMA] Remove redundant bucket_count variable from base::Histogram.

base/metrics/bucket_ranges.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // BucketRanges stores the vector of ranges that delimit what samples are
 // tallied in the corresponding buckets of a histogram. Histograms that have
 // same ranges for all their corresponding buckets should share the same
 // BucketRanges object.
 //
 // E.g. A 5 buckets LinearHistogram with 1 as minimal value and 4 as maximal
@@ skipping 21 matching lines @@
 
   explicit BucketRanges(size_t num_ranges);
   ~BucketRanges();
 
   size_t size() const { return ranges_.size(); }
   HistogramBase::Sample range(size_t i) const { return ranges_[i]; }
   void set_range(size_t i, HistogramBase::Sample value);
   uint32 checksum() const { return checksum_; }
   void set_checksum(uint32 checksum) { checksum_ = checksum; }
 
+  // A bucket is defined by a consecutive pair of entries in |ranges|, so there
+  // is one fewer bucket than there are ranges.  For example, if |ranges| is
+  // [0, 1, 3, 7, INT_MAX], then the buckets in this histogram are
+  // [0, 1), [1, 3), [3, 7), and [7, INT_MAX).
+  size_t bucket_count() const { return ranges_.size() - 1; }
+
   // Checksum methods to verify whether the ranges are corrupted (e.g. bad
   // memory access).
   uint32 CalculateChecksum() const;
   bool HasValidChecksum() const;
   void ResetChecksum();
 
   // Return true iff |other| object has same ranges_ as |this| object's ranges_.
   bool Equals(const BucketRanges* other) const;
 
  private:
@@ skipping 12 matching lines @@
   DISALLOW_COPY_AND_ASSIGN(BucketRanges);
 };
 
 //////////////////////////////////////////////////////////////////////////////
 // Expose only for test.
 BASE_EXPORT_PRIVATE extern const uint32 kCrcTable[256];
 
 }  // namespace base
 
 #endif  // BASE_METRICS_BUCKET_RANGES_H_