Make LegacySetPrimaryAccount() go through SignIn()

This CL changes LegacySetPrimaryAccount() to call
PrimaAccountManager::SignIn() rather than SetAuthenticatedAccountInfo().

This is part of a series of CLs to port ChromeOS to use
PrimaryAccountMutator, to unify its behaviour with the other platforms,
as described in
https://docs.google.com/document/d/15y-Db27BV08vrIyelHB-3CwiAfDYh-FigNKGXrqSWto

Bug: 814787, 944012
Change-Id: Idf67c8238dfef3991e6245018c0bc1f2b244f6cd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1651732
Commit-Queue: Henrique Ferreiro <hferreiro@igalia.com>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#669201}
5 files changed