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

device/generic_sensor/platform_sensor_polling_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_polling_mac.h"
+
+#include "device/generic_sensor/platform_sensor_mac.h"
+
+namespace device {
+
+SensorsPollingThreadMac::SensorsPollingThreadMac(const char* name)
+    : base::Thread(name) {}
+
+SensorsPollingThreadMac::~SensorsPollingThreadMac() = default;
+
+void SensorsPollingThreadMac::BeginPollingSensor(
+    PlatformSensorMac* sensor,
+    const PlatformSensorConfiguration& configuration) {
+  auto it = sensors_.find(sensor);
+  if (it != sensors_.end())
+    return;
+
+  std::unique_ptr<base::RepeatingTimer> timer(new base::RepeatingTimer);
+  timer->Start(FROM_HERE, base::TimeDelta::FromMicroseconds(
+                              base::Time::kMicrosecondsPerSecond /
+                              configuration.frequency()),
+               sensor, &PlatformSensorMac::UpdateReading);
+  sensors_.insert({sensor, std::move(timer)});
+}
+
+void SensorsPollingThreadMac::StopPollingSensor(PlatformSensorMac* sensor) {
+  auto it = sensors_.find(sensor);
+  if (it == sensors_.end())
+    return;
+
+  it->second.reset();
+  sensors_.erase(it);
+}
+
+}  // namespace device