Add rounding to the GRAVITY sensor.

For privacy, the accuracy of precision of acceleration is rounded to
0.1 m/s². The new sensor "GRAVITY" is based on acceleration, but
rounding is missing.

This patch applies the same rounding for both and removes the
"default" case. This will force creator of new SensorType to make
an explicit decision in the future.

+CC engedy@ who discussed this during security/privacy meeting.

Bug: 1163993
Change-Id: I8d3ff04421794aed1899711f018bc579d2bf8200
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2684575
Commit-Queue: Arthur Sonzogni <arthursonzogni@chromium.org>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Reviewed-by: Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>
Reviewed-by: Balazs Engedy <engedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#852328}

services/device/generic_sensor/platform_sensor_util.cc

@@ -101,24 +101,29 @@ void RoundOrientationEulerReading(SensorReadingXYZ* reading) {
 void RoundSensorReading(SensorReading* reading, mojom::SensorType sensor_type) {
   switch (sensor_type) {
     case mojom::SensorType::ACCELEROMETER:
-      FALLTHROUGH;
+    case mojom::SensorType::GRAVITY:
     case mojom::SensorType::LINEAR_ACCELERATION:
       RoundAccelerometerReading(&reading->accel);
       break;
+
     case mojom::SensorType::GYROSCOPE:
       RoundGyroscopeReading(&reading->gyro);
       break;
+
     case mojom::SensorType::ABSOLUTE_ORIENTATION_EULER_ANGLES:
-      FALLTHROUGH;
     case mojom::SensorType::RELATIVE_ORIENTATION_EULER_ANGLES:
       RoundOrientationEulerReading(&reading->orientation_euler);
       break;
+
     case mojom::SensorType::ABSOLUTE_ORIENTATION_QUATERNION:
-      FALLTHROUGH;
     case mojom::SensorType::RELATIVE_ORIENTATION_QUATERNION:
       RoundOrientationQuaternionReading(&reading->orientation_quat);
       break;
-    default:
+
+    case mojom::SensorType::AMBIENT_LIGHT:
+    case mojom::SensorType::MAGNETOMETER:
+    case mojom::SensorType::PRESSURE:
+    case mojom::SensorType::PROXIMITY:
       break;
   }
 }