Allow for async permission request when first accessing sensor data

[tobie]

Make sure the API is compatible with sensors which need to ask the user's permission before being used.

Proposed resolutions:

• The Generic Sensor API must be compatible with an async permissioning model.

Actions:

• Identify the best solution to communicate that the permission to access the sensor has been denied by the user agent.

[rwaldron]

The "value is null until first reading is delivered" should work really well with user permission prompting.

let geo = new Sensor.Geolocation(); // <-- this will trigger some kind of permission request to the user

geo.lat; // null until user grants permission, which might be never

geo.on("change", function() {
  // will only ever be invoked if the user grants permission, which might be never. 
});

[tobie]

Yup. Might need to emit a PERMISSION_DENIED error event of some sort.

[marcoscaceres]

I'm watching this repo, but please ping me and I'll try to help in any way I can.

[tobie]

@marcoscaceres creating a dedicated issue for discussing the Permission API: #22.

[tobie]

Depends on ongoing work on the Permission API: w3c/permissions#66