The content shell by default doesn't have a robust concept of StoragePartitions. It doesn't provide useful URLRequestContexts, doesn't seem to persist cookies, etc.

AppShell apps should be isolated from one another (something Chrome handles[1]) and have their own persistent storage (something Profile handles).

The AppIsolationHandler manifest handler is responsible for defaulting platform apps to isolated. It lives in //extensions but is added from Chrome; we should add that in AppShell as well, but it doesn't fix the above problems.

[1] https://cs.chromium.org/chromium/src/content/browser/renderer_host/render_process_host_impl.cc?gsn=IsSuitableHost&l=2850