I'm seeing geolocation failure on WebChromeClient webview in my Android app on Android 5.1.1. My Webview application has appropriate android.permission.INTERNET and android.permission.ACCESS_FINE_LOCATION permissions as well as the Javascript setting controls.
I also tried the Mapbox alternative Locate control at https://api.mapbox.com/mapbox.js/plugins/leaflet-locatecontrol/v0.43.0/L.Control.Locate.min.js with no luck. Seems to be timing out in finding location. The HTML finds location on desktop browsers and also in Firefox and Chrome mobile browsers so it seems like an issue with the WebChrome Client webview.