Create a histogram serialization mechanism in components/metrics

components/metrics/chromeos/linearhistogram_sample.h

+// Copyright 2014 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.
+
+#ifndef COMPONENTS_METRICS_CHROMEOS_LINEARHISTOGRAM_SAMPLE_H_
+#define COMPONENTS_METRICS_CHROMEOS_LINEARHISTOGRAM_SAMPLE_H_
+
+#include <string>
+
+#include "base/compiler_specific.h"
+#include "base/memory/scoped_ptr.h"
+#include "components/metrics/chromeos/metric_sample.h"
+
+namespace metrics {
+
+// Represent a linear histogram sample (called Enum too).

[Luigi Semenzato, 2014/05/08 17:19:37]

Is this really correct?  It is possible that the initial chromeos metrics code
merged enumerated histograms and linear histograms because they are similar. 
But wouldn't a linear histogram possibly have a non-zero lower bound, whereas
the enum histograms always starts at zero?

[bsimonnet, 2014/05/12 22:45:37]

I remove that comment. The README recommends not to use histograms for
enumerations so it is probably better not to mention it here.
The current code in external metrics sets min to 1 so it is probably not a good
idea so send an enum.

+// This class is meant to be used to serialize and deserialize samples to send
+// them from ChromeOS to Chrome.
+class LinearHistogramSample : public MetricSample {
+ public:
+  LinearHistogramSample(const std::string& name, int sample, int max);
+  virtual ~LinearHistogramSample();
+
+  int sample() const { return sample_; }
+  int max() const { return max_; }
+
+  // Return the serialized version of the sample in the format:
+  // linearhistogram\0|name_| |sample_| |max_|\0
+  virtual std::string ToString() const OVERRIDE;
+
+  // Deserialize a sample passed as a string.
+  // Returns a LinearHistogram if the deserialization is successful.
+  // Returns NULL if the deserialization fails.
+  // The serialized format is a list of |name|, |sample|, |max|
+  // separated by space.
+  static scoped_ptr<LinearHistogramSample> ReadLinearHistogram(
+      const std::string& serialized_histogram);
+
+ private:
+  const int sample_;
+  const int max_;
+
+  DISALLOW_COPY_AND_ASSIGN(LinearHistogramSample);
+};
+
+}  // namespace metrics
+
+#endif  // COMPONENTS_METRICS_CHROMEOS_LINEARHISTOGRAM_SAMPLE_H_