[sensors] [mac] Implement ambient light sensor for macOS

device/generic_sensor/platform_sensor_mac.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_PLATFORM_SENSOR_MAC_H_
+#define DEVICE_GENERIC_SENSOR_PLATFORM_SENSOR_MAC_H_
+
+#include "base/timer/timer.h"
+#include "device/generic_sensor/platform_sensor.h"
+
+namespace base {
+class SingleThreadTaskRunner;
+}
+
+namespace device {
+
+class PlatformSensorMac : public PlatformSensor {

[Mikhail, 2016/09/19 06:25:18]

this class actually does not have any deps to Mac, on the other hand
implementations on Linux/CrOS would also need a polling sensor primitive
(maksim@ isn't it?) so maybe it's worth renaming it to 'PollingPlatformSensor'
or smth like that.

[maksims (do not use this acc), 2016/09/20 09:51:35]

Ouch, I've just noticed this. Yes, right. I have almost the same implementation,
but without timers. We can have only this one then!

+ public:
+  PlatformSensorMac(
+      mojom::SensorType type,
+      mojo::ScopedSharedBufferMapping mapping,
+      PlatformSensorProvider* provider,
+      scoped_refptr<base::SingleThreadTaskRunner> polling_thread_task_runner);
+  bool StartSensor(const PlatformSensorConfiguration& configuration) override;

[Mikhail, 2016/09/19 06:25:18]

can all these methods be protected (as accessed either via PlatformSensor
interface or from inside the object itself)?

+  void StopSensor() override;
+
+  virtual void UpdateReading() = 0;
+
+ protected:
+  ~PlatformSensorMac() override;
+  scoped_refptr<base::SingleThreadTaskRunner> polling_thread_task_runner_;
+  scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner_;
+  std::unique_ptr<base::RepeatingTimer> timer_;

[Mikhail, 2016/09/19 06:25:18]

base::RepeatingTimer timer_; // like in example from timer.h, thus we can also
obviate re-creating it on heap every StartSensor call.

+
+ private:
+  void BeginPoll(const PlatformSensorConfiguration& configuration);
+  void StopPoll();
+
+  DISALLOW_COPY_AND_ASSIGN(PlatformSensorMac);
+};
+
+}  // namespace device
+
+#endif  // DEVICE_GENERIC_SENSOR_PLATFORM_SENSOR_MAC_H_