Delay Lacros startup until owner_id is fetched

BrowserInitParams contains information whether the current user in
Ash is the device owner. This information is read from UserManager.
Unfortunately reading this information has a race condition, since
the owner account id is set at a later point in Ash startup. So an
async method for fetching the owner account ID was introduced to the
UserManager in crrev/c/4507352.

This CL makes use of the async API and delays the creation of Browser
InitParams until the owner is initialized.

Bug: b/245337406
Change-Id: I13520b98932971a7ab05dbccf3ab81a5eddb7f30
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4509343


Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Commit-Queue: Bastian Kersting <bkersting@google.com>
Cr-Commit-Position: refs/heads/main@{#1146411}