Where in the source code does the Google VR plugin get the device rotation?

I’m trying to understand how the Google Cardboard plugin works, but I don’t understand where the plugin gets the gyroscope data from the phone. The “normal” way to get the gyroscope data is by using SensorManager, provided by the Android framework. However, Unreal uses something else.
Does anyone know how Unreal handles the gyroscope and uses the data to get the direction the user is looking at?

UE4 reads SensorManager in LaunchAndroid.cpp.