[sensors] Ambient light sensor implementation for ChromeOS and Linux.

device/generic_sensor/iio/sensor_data_iio.h

+// Copyright 2016 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 DEVICE_GENERIC_SENSOR_IIO_SENSOR_DATA_IIO_H_
+#define DEVICE_GENERIC_SENSOR_IIO_SENSOR_DATA_IIO_H_
+
+#include "device/generic_sensor/public/interfaces/sensor.mojom.h"
+
+namespace device {
+
+// This structure represents a context that is used to
+// create a type specific SensorReader and a concrete
+// sensor that uses the SensorReader to read sensor
+// data from files specified in the |sensor_file_names|.
+struct SensorDataIio {
+  // Provides a base path to all sensors.
+  const base::FilePath::CharType* base_path_sensor_iio;
+  // Provides an array of sensor file names to be searched for.
+  const char** sensor_file_names[3];

[Reilly Grant (use Gerrit), 2016/10/24 21:49:27]

Since we have a function that builds these structures I'd rather we use
std::vector<std::string> here and not have to use the length fields below.

[maksims (do not use this acc), 2016/10/25 06:23:54]

Basically, the data is static and is defined only once. What is more, it is a
convenient to know how many sensor files must be read. According to this data,
we set a certain number of paths, which correspon how many field of
SensorReading will be filled in with data. 

In the future, we will add more sensors, which will have, for example, 3 files
to be read from. Thus, I would prefer to use this implementation, otherwise
vector of vectors will have to be used.  

[Reilly Grant (use Gerrit), 2016/10/25 17:36:25]

A vector of vectors is the right data structure for this.

+  // Number of files in each |sensor_file_names| array.
+  size_t sensor_file_names_cols;
+  // Number of arrays in |sensor_file_names|.
+  // Corresponds to the sensor reading fields number.
+  size_t sensor_file_names_rows;
+  // Reporting mode of a sensor.
+  mojom::ReportingMode reporting_mode;
+  // Default configuration of a sensor.
+  PlatformSensorConfiguration default_configuration;
+};
+
+// Initializes a sensor type specific data.
+bool InitSensorData(mojom::SensorType type, SensorDataIio* data);
+
+}  // namespace device
+
+#endif  // DEVICE_GENERIC_SENSOR_IIO_SENSOR_DATA_IIO_H_