Offline Demo Mode enrollment times out waiting for GetServerBackedStateKeys and fails with NO_STATE_KEYS, if the device has been offline since boot.

This might only repro if FRE is on, which is true if chrome is build with `is_official_build = true`.

The GetServerBackedStateKeys dbus timeout is expected when there hasn't been network connectivity since boot:
https://cs.chromium.org/chromium/src/chromeos/dbus/session_manager_client.cc?type=cs&q=TIMEOUT_INFINITE+session_manager_client&sq=package:chromium&g=0&l=389

But the keys are required for FRE:
https://cs.chromium.org/chromium/src/chrome/browser/chromeos/policy/enrollment_handler_chromeos.cc?type=cs&sq=package:chromium&g=0&l=380

Connecting the device to a network will allow the retry attempt to succeed, but that partly defeats the purpose of an offline mode.

Relevant logs:

[3257:3257:0827/140338.870793:VERBOSE1:demo_setup_controller.cc(155)] Starting demo mode enrollment offline
[3257:3257:0827/140721.340531:ERROR:object_proxy.cc(615)] Failed to call method: org.chromium.SessionManagerInterface.GetServerBackedStateKeys: object_path= /org/chromium/SessionManager: org.freedesktop.DBus.Error.NoReply: Message did not receive a reply (timeout by message bus)
[3257:3257:0827/140721.340604:WARNING:server_backed_state_keys_broker.cc(75)] Failed to obtain server-backed state keys.
[3257:3257:0827/140721.340656:WARNING:enrollment_handler_chromeos.cc(813)] Enrollment failed: 1, client: 0, validation: 0, store: 0, lock: 0
[3257:3257:0827/140721.340731:ERROR:demo_setup_controller.cc(347)] EnrollmentError: status: 1 client_status: 0 store_status: 0 validation_status: 0 lock_status: 0 fatal=0