crOS Account Manager: Fix sign-in error notification

Display a notification informing users about Chrome OS's change in
sign-in behaviour, if there are any unmigrated accounts in Chrome OS
Account Manager. This notification should supersede the default
re-authentication notification.

Bug: 962287
Change-Id: Ib8bffa6756727f77e6abe77f21a0b865b94824a5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1615142
Reviewed-by: David Roger <droger@chromium.org>
Commit-Queue: Kush Sinha <sinhak@chromium.org>
Cr-Commit-Position: refs/heads/master@{#660792}
3 files changed