Add RELATIVE_ORIENTATION sensor implementation on macOS to //device/generic_sensor

device/generic_sensor/platform_sensor.cc

Index: device/generic_sensor/platform_sensor.cc
diff --git a/device/generic_sensor/platform_sensor.cc b/device/generic_sensor/platform_sensor.cc
index 34afa2d69987ab49b01dcf8041945c523c9f0b02..95b6bc86e3f1f65edd21a3b6edd03088bb9ab0a9 100644
--- a/device/generic_sensor/platform_sensor.cc
+++ b/device/generic_sensor/platform_sensor.cc
@@ -90,6 +90,13 @@ void PlatformSensor::RemoveClient(Client* client) {
   }
 }
 
+bool PlatformSensor::GetLatestReading(SensorReading* result) {
+  const SensorReadingSharedBuffer* buffer =
+      static_cast<const SensorReadingSharedBuffer*>(
+          shared_buffer_mapping_.get());
+  return GetSensorReadingFromBuffer(buffer, result);
+}
+
 void PlatformSensor::UpdateSensorReading(const SensorReading& reading,
                                          bool notify_clients) {
   ReadingBuffer* buffer =