I'm working on LauncherItemController::Activate / ShelfItemDelegate::ItemSelected refactoring at the moment.
That doesn't exactly ChromeLauncherController::LaunchApp / ChromeLauncherController::ActivateApp, but it'll help.
Any help in this area is greatly appreciated.

Is there a meta-bug tracking app list defects in mash? (like shelf  Issue 557406  and  Issue 681072 ).
Perhaps we should re-open  Issue 557408 ...

There's issue 678705, which covers all chrome <-> ash communication changes necessary for our 30 min casual browsing Q1 OKR. No app-list specific master bug that I know of. We could create it, but we don't have to do all of it for Q1. It would be good to identify the parts that we do need to do for Q1 (this issue?) and log bugs under issue 678705.

I wouldn't say that this is blocked on  Issue 557406 . We don't need all mash shelf functionality to launch apps from the app list.

As of r463266 this morning, on device Pixel 1 with --mash, I cannot launch any app from the app list, including the Files app. I don't see anything interesting in the logs.

On desktop I can launch the Files app but not the web store app. On desktop I see this:

[11953:11953:0410/092813.400805:ERROR:chrome_launcher_controller_mus.cc(87)] Not implemented reached in virtual void ChromeLauncherControllerMus::ActivateApp(const std::string &, ash::ShelfLaunchSource, int)

Seems fixed in Tot.

Test the rest of launcher in Mash.