Use TYPICAL_PROXIMITY_THRESHOLD instead of mProximitySensor.getMaximumRange()

Presto's proximity sensor returns values: 0.0f(near) or 5.0f(far). 
mProximitySensor.getMaximumRange() must return proximity sensor's availible range, but it always return 0, so mProximityThreshold is also 0. 

So boolean positive = distance >= 0.0f && distance < mProximityThreshold;  positive will never be 
true.
The cause of this problem is proprietary sensor.msm8660.so, it must set proper Range and Resolution for proximity sensor.