Move CachedRanges out and add support for checksum.

base/metrics/bucket_ranges.h

Index: base/metrics/bucket_ranges.h
===================================================================
--- base/metrics/bucket_ranges.h	(revision 0)
+++ base/metrics/bucket_ranges.h	(working copy)
@@ -0,0 +1,69 @@
+// 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
+// value will need a BucketRanges with 6 ranges:
+// 0, 1, 2, 3, 4, INT_MAX
+//
+// TODO(kaiwang): Currently we keep all negative values in 0~1 bucket. Consider
+// changing 0 to INT_MIN.
+
+#ifndef BASE_METRICS_BUCKET_RANGES_H_
+#define BASE_METRICS_BUCKET_RANGES_H_
+
+#include <vector>
+
+#include "base/base_export.h"
+#include "base/basictypes.h"
+#include "base/gtest_prod_util.h"
+#include "base/metrics/histogram_base.h"
+
+namespace base {
+
+class BASE_EXPORT_PRIVATE BucketRanges {
+ public:
+  typedef std::vector<HistogramBase::Sample> Ranges;
+
+  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; }
+
+  // Checksum methods to verify whether the ranges are corrupted (e.g. bad
+  // memory access).
+  uint32 CalculateChecksum();
+  bool HasValidChecksum();
+  void ResetChecksum();
+
+  // Return true iff |other| object has same ranges_ as |this| object's ranges_.
+  bool Equals(const BucketRanges* other) const;
+
+ private:
+  // A monotonically increasing list of values which determine which bucket to
+  // put a sample into.  For each index, show the smallest sample that can be
+  // added to the corresponding bucket.
+  Ranges ranges_;
+
+  // Checksum for the conntents of ranges_.  Used to detect random over-writes
+  // of our data, and to quickly see if some other BucketRanges instance is
+  // possibly Equal() to this instance.
+  // TODO(kaiwang): Consider change this to uint64. Because we see a lot of
+  // noise on UMA dashboard.
+  uint32 checksum_;
+
+  DISALLOW_COPY_AND_ASSIGN(BucketRanges);
+};
+
+}  // namespace base
+
+#endif  // BASE_METRICS_BUCKET_RANGES_H_