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

device/generic_sensor/platform_sensor_provider_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_provider_mac.h"
+
+#include <list>
+
+#include "base/memory/singleton.h"
+#include "base/threading/thread.h"
+#include "device/generic_sensor/platform_sensor_ambient_light_mac.h"
+
+namespace device {
+
+// static
+PlatformSensorProvider* PlatformSensorProvider::GetInstance() {
+  return PlatformSensorProviderMac::GetInstance();
+}
+
+// static
+PlatformSensorProviderMac* PlatformSensorProviderMac::GetInstance() {
+  return base::Singleton<
+      PlatformSensorProviderMac,
+      base::LeakySingletonTraits<PlatformSensorProviderMac>>::get();
+}
+
+PlatformSensorProviderMac::PlatformSensorProviderMac() = default;
+
+PlatformSensorProviderMac::~PlatformSensorProviderMac() {
+  if (polling_thread_)
+    polling_thread_->Stop();
+}
+
+scoped_refptr<PlatformSensor> PlatformSensorProviderMac::CreateSensorInternal(
+    mojom::SensorType type,
+    mojo::ScopedSharedBufferMapping mapping,
+    uint64_t buffer_size) {
+  if (!polling_thread_) {
+    polling_thread_.reset(new base::Thread("Sensor poller Mac"));

[Robert Sesek, 2016/09/20 14:25:21]

If we do use polling polling, does this really need to be on its own dedicated
thread? Why can't this be on a worker pool task runner?

+    if (!polling_thread_->Start()) {
+      LOG(WARNING) << "Couldn't start the polling thread.";
+      return nullptr;
+    }
+  }
+  // Create Sensors here.
+  switch (type) {
+    case mojom::SensorType::AMBIENT_LIGHT:
+      return new PlatformSensorAmbientLightMac(type, std::move(mapping),
+                                               buffer_size, this,
+                                               polling_thread_->task_runner());
+    default:
+      NOTIMPLEMENTED();
+      return nullptr;
+  }
+}
+
+}  // namespace device