Use "navigator.permissions" to detect geolocation support

[tmcw]

Due to new security restrictions, the presence of navigator.geolocation is no longer a complete indication of geolocation support: the navigator.permissions API allows one to query for access to the API. This PR moves geolocation support checking to the GeolocationControl in order to support this asynchronous API.

Testing plan:

1. npm run start-debug
2. edit /etc/hosts to give your localhost another creative name, since the Chrome HTTPS rule whitelists localhost
3. confirm that the control is not visible on the alternative name, but is visible on localhost

Implementation notes:

Since the permissions API is async and is not instant, this approach caches the result. I have not found any cases where the result will change.

Launch Checklist

Fixes #3568 - waiting on #3497 because this needs to move the geolocation detection into the geocodercontrol itself. Actionable - workingonit.

• briefly describe the changes in this PR
• write tests for all new functionality
• document any changes to public APIs
• post benchmark scores
• manually test the debug page

[mourner]

we should move the geolocation detection to the control
itself

Yep! This will allow us to consistently disable geolocation if it's not supported, no matter at what time the geolocation control is added.

[tmcw]

This is now ready for review @mourner @lucaswoj

[mourner]

I think it would be slightly cleaner to call the callback in any outcome, and move responsibility for checking supportsGeolocation value to _setupUI:

function checkGeolocationSupport(callback) {
    if (supportsGeolocation !== undefined) {
        callback();

    } else if (window.navigator.permissions !== undefined) {
        window.navigator.permissions.query({name: 'geolocation'}).then((p) => {
            supportsGeolocation = p.state !== 'denied';
            callback();
        });
    } else {
        supportsGeolocation = !!window.navigator.geolocation;
        callback();
    }
}

[tmcw]

Already tried both variations, but I'm flexible. I'll switch it to the suggested style.

[mourner]

BTW, should we limit the line width to 70 chars in comments like this? IMHO increasing the limit would help readability.

[tmcw]

Not sure how you're set up, but in vim-land I never use wrapping so cutting lines like this is more readable.

[mourner]

I don't use wrapping too, it just that 70 seems too short, given that we use up to 120 for the code.