Reland of: chromeos: Add CPU temperature reader

chromeos/system/cpu_temperature_reader.h

Index: chromeos/system/cpu_temperature_reader.h
diff --git a/chromeos/system/cpu_temperature_reader.h b/chromeos/system/cpu_temperature_reader.h
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+// Copyright 2017 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 CHROMEOS_SYSTEM_CPU_TEMPERATURE_READER_H_
+#define CHROMEOS_SYSTEM_CPU_TEMPERATURE_READER_H_
+
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "base/files/file_path.h"
+#include "base/macros.h"
+#include "chromeos/chromeos_export.h"
+
+namespace chromeos {
+namespace system {
+
+// Used to read CPU temperature info from sysfs hwmon.
+class CHROMEOS_EXPORT CPUTemperatureReader {
+ public:
+  // Contains info from a CPU temperature sensor.
+  struct CPUTemperatureInfo {
+    CPUTemperatureInfo();
+    ~CPUTemperatureInfo();
+
+    bool operator<(const CPUTemperatureInfo& other) const {
+      return std::make_pair(label, temp_celsius) <
+             std::make_pair(other.label, other.temp_celsius);
+    }
+
+    // The temperature read by a CPU temperature sensor in degrees Celsius.
+    double temp_celsius;
+
+    // The name of the CPU temperature zone monitored by this sensor. Used to
+    // identify the source of each temperature reading. Taken from sysfs "name"
+    // or "label" field, if it exists.
+    std::string label;
+  };
+
+  CPUTemperatureReader();
+  ~CPUTemperatureReader();
+
+  void set_hwmon_dir_for_test(const base::FilePath& dir) { hwmon_dir_ = dir; }
+
+  // Reads temperature from each thermal sensor of the CPU. Returns a vector
+  // containing a reading from each sensor. This is a blocking function that
+  // should be run on a thread that allows blocking operations.
+  std::vector<CPUTemperatureInfo> GetCPUTemperatures();
+
+ private:
+  // Sysfs hwmon directory path.
+  base::FilePath hwmon_dir_;
+
+  DISALLOW_COPY_AND_ASSIGN(CPUTemperatureReader);
+};
+
+}  // namespace system
+}  // namespace chromeos
+
+#endif  // CHROMEOS_SYSTEM_CPU_TEMPERATURE_READER_H_