GitLab

Move away from OAuth2TokenService and SigninManagerBase by implementing
IdentityManager::Observer and using Identity Service's APIs only (i.e.
IdentityManager, PrimaryAccessTokenFetcher).

Bug: 905689
Change-Id: I68e971ddf8a23987abfdadb8e2daf7b17a4a6ddb
Reviewed-on: https://chromium-review.googlesource.com/c/1340315Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Commit-Queue: Mario Sanchez Prada <mario@igalia.com>
Cr-Commit-Position: refs/heads/master@{#611044}