[Autofill Assistant] Make the default switch preference consistent

Make the default switch preference in settings is true as we used in
AutofillAssistantFacade.isConfigured.

This CL also refactors the code to clear class scope and dependency.

Bug: 806868
Change-Id: I85326c7075d1f353b301934f20a3e2aef127ecc5
Reviewed-on: https://chromium-review.googlesource.com/c/1338470
Commit-Queue: Ganggui Tang <gogerald@chromium.org>
Reviewed-by: Mathias Carlen <mcarlen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608780}
5 files changed