interact with map async after map has loaded

[jfreeland]

It's probably at least in part because I'm new to flutter and flutter_google_maps but after a bit of reading through the code and examples I wasn't able to find the best way to run a separate function, without user interaction, after the map has loaded. For example, to load a dynamic list of markers from http.

If this is possible it might be handy to update the example or add a new one showing reading a couple markers from a separate file and adding the new markers dynamically.

For instance, google_maps_flutter has an onMapCreated field where you can specify the next function to run.