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

device/generic_sensor/platform_sensor_mac.cc

+// 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.
+
+#include "device/generic_sensor/platform_sensor_mac.h"
+
+#include "base/message_loop/message_loop.h"
+
+namespace device {
+
+PlatformSensorMac::PlatformSensorMac(
+    mojom::SensorType type,
+    mojo::ScopedSharedBufferMapping mapping,
+    PlatformSensorProvider* provider,
+    const scoped_refptr<base::SingleThreadTaskRunner>&
+        polling_thread_task_runner)
+    : PlatformSensor(type, std::move(mapping), provider),
+      polling_thread_task_runner_(polling_thread_task_runner),
+      ui_task_runner_(base::MessageLoop::current()->task_runner()) {}
+
+PlatformSensorMac::~PlatformSensorMac() {
+  timer_.reset();

[Mikhail, 2016/09/16 16:23:54]

won't it get reset automatically when deleted?

+}
+
+bool PlatformSensorMac::StartSensor(
+    const PlatformSensorConfiguration& configuration) {
+  polling_thread_task_runner_->PostTask(
+      FROM_HERE, base::Bind(&PlatformSensorMac::BeginPoll,
+                            base::Unretained(this), configuration));
+  return true;
+}
+
+void PlatformSensorMac::BeginPoll(
+    const PlatformSensorConfiguration& configuration) {

[Mikhail, 2016/09/16 16:23:54]

DCHECK to make sure this is a polling thread would be advisable here

+  timer_.reset(new base::RepeatingTimer());
+  timer_->Start(FROM_HERE, base::TimeDelta::FromMicroseconds(
+                               base::Time::kMicrosecondsPerSecond /
+                               configuration.frequency()),
+                this, &PlatformSensorMac::UpdateReading);
+}
+
+void PlatformSensorMac::StopSensor() {
+  polling_thread_task_runner_->PostTask(
+      FROM_HERE,
+      base::Bind(&PlatformSensorMac::StopPoll, base::Unretained(this)));

[Mikhail, 2016/09/16 16:23:54]

base::Unretained(this) can lead to raise condition if scheduled task is called
after 'this' gets deleted.

+}
+
+void PlatformSensorMac::StopPoll() {
+  timer_.reset();
+}
+
+}  // namespace device