[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() {}

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

nit: = 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"));
+    if (!polling_thread_->Start()) {

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

For the record: 
in future we can add smth like 'protected virtual void
PlatformSensorProviderBase::AllSensorsRemoved() {}' and call it from
'PlatformSensorProviderBase::RemoveSensor' when there are no sensors left. It'll
be overridden in this class so that polling thread is terminated when it is not
needed.

+      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