Some things are needed to be able to run regular flutter apps on top of other shell client (meaning that there's no designated application that serves as the shell client).

• rename ivi-homescreen to something more suitable like a flutter-ed. This has to happen in ivi-homescreen as to avoid having two homescreen binaries as they can't be installed side-by side. Also rename the service name. The alternative would be to rename qt homescreen to something else. Maybe there are other alternatives?
• add another flutter-gallery recipe, which is basically is the older ivi-homescreen. This recipe installs the the systemd service file and uses the correct path to the flutter embedder. This serves as a basis/basic recipe for GSOC clients to use. Just copy this recipe put your own SRC_URI and that's it.
• the embedder needs to handle correctly the situation where it's just a single application. I've currently did some hacks/changes in it to allow me to run it. I'll post soon a MR for upstream to have these in. I just need to try both situations to verify nothing's broken with them (By both I mean the flutter embedder be also a shell client, not just a regular lcient). I've also found some stuff in the compositor that could be helpful to improve the protocol. but I'll leave this aside for the time being (and open another JIRA for that).

Fyi, I had to hack ivi-homescreen bbappend recipe (avoid installing homescreen service) and ivi-homescreen to generate a different binary name to be able to run it + some minor changes in the code to avoid a bind by default to the agl-shell protocol.

/cc jsmoeller scottm