private String mGeolocationOrigin;
private GeolocationPermissions.Callback mGeolocationCallback;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    // other setup

    myWebView.setWebChromeClient(new MyWebChromeClient());
}

public class MyWebChromeClient extends WebChromeClient {
    @Override
    public void onGeolocationPermissionsShowPrompt(String origin,
                                                   GeolocationPermissions.Callback callback) {
        // Geolocation permissions coming from this app's Manifest will only be valid for devices with API_VERSION < 23.
        // On API 23 and above, we must check for permission, and possibly ask for it.
        final String permission = Manifest.permission.ACCESS_FINE_LOCATION;
        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.M ||
                ContextCompat.checkSelfPermission(MainActivity.this, permission) == PackageManager.PERMISSION_GRANTED) {
            // we're on SDK < 23 OR user has already granted permission
            callback.invoke(origin, true, false);
        } else {
            if (ActivityCompat.shouldShowRequestPermissionRationale(MainActivity.this, permission)) {
                // user has denied this permission before and selected [/] DON'T ASK ME AGAIN
                // TODO Best Practice: show an AlertDialog explaining why the user could allow this permission, then ask again
            } else {
                // ask the user for permissions
                ActivityCompat.requestPermissions(MainActivity.this, new String[] {permission}, RP_ACCESS_LOCATION);
                mGeolocationOrigin = origin;
                mGeolocationCallback = callback;
            }
        }
    }
}