Update IdentityManager to own AccountTrackerService.

With this change, AccountTrackerService is now constructed only when
creating an IdentityManager, eliminating the need for
AccountTrackerService factories.

Change-Id: I18a527d6c56446ced653aca9c7ff42a9c657065b
Bug: 939372
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1549083
Reviewed-by: David Roger <droger@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Commit-Queue: Lowell Manners <lowell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653112}
26 files changed