Create a histogram serialization mechanism in components/metrics

components/metrics/chromeos/metric_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_METRIC_SAMPLE_H_
+#define COMPONENTS_METRICS_CHROMEOS_METRIC_SAMPLE_H_
+
+#include <string>
+
+#include "base/macros.h"
+
+namespace metrics {
+
+// Abstract class representing a metric sample (single measures).
+// This class and its subclasses are used by libmetrics (ChromeOS) to serialize
+// and deserialize measurements to send them to a metrics sending service.
+// It is meant to be a simple container with serialization functions.
+class MetricSample {
+ public:
+  // Types of metric sample used.
+  enum SampleType {
+    CRASH,
+    HISTOGRAM,
+    LINEAR_HISTOGRAM,
+    SPARSE_HISTOGRAM,
+    USER_ACTION
+  };
+
+  MetricSample(SampleType sample_type, const std::string& metric_name);
+  virtual ~MetricSample();
+
+  // Return true if the sample is valid (can be serialized without ambiguity).

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

What does this mean?

[bsimonnet, 2014/05/08 20:02:58]

As the fields are separated by spaces, we do not want to have spaces in the
histogram names (or \0) as it would make it impossible for the sample to be
deserialized.

+  //
+  // This function should be used to filter bad samples before serializing them
+  // to disk.

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

Maybe "to disk" is assuming too much here?

+  virtual bool IsValid() const;
+
+  SampleType type() const { return type_; }
+  const std::string& name() const { return name_; }
+
+  // Return a serialized version of the sample.
+  //
+  // This function should be overriden by subclasses to define their own
+  // serialization format.
+  // The general serialized message is:
+  // |sampletype|,\0,<sample type specific serialized data>,\0
+  //
+  // The format is akward but it is implemented independently in both chrome os

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

typo: awkward

What does "implemented independently" mean?

[bsimonnet, 2014/05/08 20:02:58]

Two different piece of code that are not synchronized or tested together.

The real comment should be:
The serialization mechanism is implemented on Chrome OS and deserialization
mechanism is implemented on Chrome. It is not easy to change both
implementations at the same time and to make sure that on every system the same
version will be used.

+  // and chrome. We will keep it for now.
+  virtual std::string ToString() const;
+
+ private:
+  const SampleType type_;
+  const std::string name_;
+
+  DISALLOW_COPY_AND_ASSIGN(MetricSample);
+};
+
+}  // namespace metrics
+
+#endif  // COMPONENTS_METRICS_CHROMEOS_METRIC_SAMPLE_H_