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

device/generic_sensor/polling_platform_sensor.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/polling_platform_sensor.h"
+
+#include "base/message_loop/message_loop.h"
+
+namespace device {
+
+PollingPlatformSensor::PollingPlatformSensor(
+    mojom::SensorType type,
+    mojo::ScopedSharedBufferMapping mapping,
+    PlatformSensorProvider* provider,
+    scoped_refptr<base::SingleThreadTaskRunner> polling_thread_task_runner)
+    : PlatformSensor(type, std::move(mapping), provider),
+      polling_thread_task_runner_(std::move(polling_thread_task_runner)),
+      ui_task_runner_(base::MessageLoop::current()->task_runner()) {}
+
+PollingPlatformSensor::~PollingPlatformSensor() = default;
+
+bool PollingPlatformSensor::StartSensor(
+    const PlatformSensorConfiguration& configuration) {
+  polling_thread_task_runner_->PostTask(
+      FROM_HERE,
+      base::Bind(&PollingPlatformSensor::BeginPoll, this, configuration));
+  return true;
+}
+
+void PollingPlatformSensor::BeginPoll(
+    const PlatformSensorConfiguration& configuration) {
+  DCHECK(polling_thread_task_runner_->BelongsToCurrentThread());
+  timer_.Start(FROM_HERE, base::TimeDelta::FromMicroseconds(

[maksims (do not use this acc), 2016/09/21 08:20:14]

You cannot create timer on one thread and kill it on another.
PollingPlatformSensor::~PollingPlatformSensor() kill the timer on another
thread. It's better not to use PostTask here. Just PostTask your actual task in
UpdateReading().

+                              base::Time::kMicrosecondsPerSecond /
+                              configuration.frequency()),
+               this, &PollingPlatformSensor::UpdateReading);
+}
+
+void PollingPlatformSensor::StopSensor() {
+  polling_thread_task_runner_->PostTask(
+      FROM_HERE, base::Bind(&PollingPlatformSensor::StopPoll, this));
+}
+
+void PollingPlatformSensor::StopPoll() {
+  DCHECK(polling_thread_task_runner_->BelongsToCurrentThread());
+  timer_.Stop();
+}
+
+}  // namespace device