Create a histogram serialization mechanism in components/metrics

components/metrics/metric_sample_chromeos.h

Index: components/metrics/metric_sample_chromeos.h
diff --git a/components/metrics/metric_sample_chromeos.h b/components/metrics/metric_sample_chromeos.h
new file mode 100644
index 0000000000000000000000000000000000000000..9c296677574acc988dbf2f7ea8a59c0c41bd8688
--- /dev/null
+++ b/components/metrics/metric_sample_chromeos.h
@@ -0,0 +1,60 @@
+// 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_METRIC_SAMPLE_CHROMEOS_H_
+#define COMPONENTS_METRICS_METRIC_SAMPLE_CHROMEOS_H_
+
+#include <string>
+
+#include "base/base_export.h"
+#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 BASE_EXPORT MetricSample {
+ public:
+  // Types of metric sample used.
+  enum SampleType {
+    CRASH,
+    HISTOGRAM,
+    LINEAR_HISTOGRAM,
+    SPARSE_HISTOGRAM,
+    USER_ACTION
+  };
+  explicit MetricSample(SampleType type, const std::string& metric_name);

[Ben Chan, 2014/04/18 20:27:08]

explicit is not needed when there are two or more arguments

+  virtual ~MetricSample();
+
+  // Returns true if the sample is valid (can be serialized without ambiguity).
+  //
+  // This function should be used to filter bad samples before serializing them
+  // to disk.
+  virtual bool IsValid() const;
+  SampleType type() const { return type_; }
+  std::string name() const { return name_; }

[Ben Chan, 2014/04/18 20:27:08]

why not "const std::string& name() const"

+
+  // Returns 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
+  // 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_METRIC_SAMPLE_CHROMEOS_H_