I have a GPS app that already requests ACCESS_FINE_LOCATION permission in the manifest, now I want to add a library (MoPub) that requires ACCESS_COARSE_L
Depends on your need.
Permission wise, ACCESS_FINE_LOCATION includes ACCESS_COARSE_LOCATION. However, there is a catch:
ACCESS_COARSE_LOCATION gives you last-known location which is battery friendly
https://developer.android.com/training/location/retrieve-current.html#setup
For example, if your app does something like location-based recommendations, last-known location is good enough.
This has a dependency on Google Play Services
However, if you need something like live/ real-time location like Pokemon Go, use ACCESS_FINE_LOCATION
It gives you live/ real-time location. You'll need to use a LocationListener
Last time I checked, this does not require Google Play Services