Settings Split: Use default settings when there is no pref service

Bug: b/241965700
Change-Id: I7e12f6c0a791e48645ffd1c6841e0f14d6152774
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4327372


Commit-Queue: David Padlipsky <dpad@google.com>
Reviewed-by: Michael Checo <michaelcheco@google.com>
Cr-Commit-Position: refs/heads/main@{#1118886}