Add TYPE_HEADING sensor type definitions.

Bug: 189983308
Test: Presubmits
Change-Id: I74186ac6685a376158101f65d2687f1905c09814
diff --git a/include/hardware/sensors.h b/include/hardware/sensors.h
index 589aba0..a5ae086 100644
--- a/include/hardware/sensors.h
+++ b/include/hardware/sensors.h
@@ -191,6 +191,7 @@
 #define SENSOR_STRING_TYPE_GYROSCOPE_LIMITED_AXES       "android.sensor.gyroscope_limited_axes"
 #define SENSOR_STRING_TYPE_ACCELEROMETER_LIMITED_AXES_UNCALIBRATED "android.sensor.accelerometer_limited_axes_uncalibrated"
 #define SENSOR_STRING_TYPE_GYROSCOPE_LIMITED_AXES_UNCALIBRATED "android.sensor.gyroscope_limited_axes_uncalibrated"
+#define SENSOR_STRING_TYPE_HEADING                      "android.sensor.heading"
 
 /**
  * Values returned by the accelerometer in various locations in the universe.