The singleton `MGLAccountManager` wants to be the sole arbiter of the access token, but each instance of `mbgl::Map` (`mbgl::DefaultFileSource` in #1607) has its own copy of the access token. Now `MGLMapView` observes for changes to the `MGLAccountManager`’s access token and synchronizes `mbgl::Map` with it.
`-pauseMetricsCollection` and `-resumeMetricsCollection` were originally introduced to mitigate concerns around battery usage, but `MGLMapboxEvents` has since evolved to tread much lighter on the battery. There’s no longer any need for the client to call these methods directly. The iOS test project now includes MGLMapboxEvents.h explicitly to avoid having to package a header that will go unused.
`MGLAccountManager` is now guaranteed to initialize without the code ever making any mention of it. It also is guaranteed to be set up before `MGLMapboxMetrics` but will definitely cause `MGLMapboxMetrics` to be set up on the main thread if the access token is set in Info.plist.
That way there’s no ambiguity about when you should call things like `+[MGLAccountManager setMapboxMetricsEnabledSettingShownInApp:]`. In fact, that method is now deprecated because it’s so easy to call in the wrong place.
Fixes#1535.
The shared `MGLMapboxEvents` now owns the only instance of `MGLMetricsLocationManager`. It also owns a `MGLMapboxEventsData` object, to which all user-specific data has been relegated. This object can be built up and torn down on the fly, whenever the opt-out preference is toggled. `MGLMapboxEvents` has also given up knowledge of the access token and now queries `MGLAccountManager` for that information, which `MGLMapView` keeps up-to-date.
