Create a histogram serialization mechanism in components/metrics

base/metrics/useraction_sample_chromeos.cc

+// Copyright (c) 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.
+
+#include "base/metrics/useraction_sample_chromeos.h"
+
+#include <string>
+
+#include "base/metrics/metric_sample_chromeos.h"
+#include "base/strings/stringprintf.h"
+
+using std::string;
+
+namespace base {
+
+UserActionSample::UserActionSample(const std::string& action_name)
+    : MetricSample(MetricSample::USER_ACTION, action_name) {}
+
+UserActionSample* UserActionSample::ReadUserAction(const std::string& action) {
+  return new UserActionSample(action);
+}
+
+UserActionSample::~UserActionSample() {}
+
+string UserActionSample::ToString() const {
+  return StringPrintf("useraction%c%s%c", '\0', name_.c_str(), '\0');
+}
+}  // namespace base