Add IdentityManager::Observer::On{Start,End}BatchOfRefreshTokenStateChanges

This mirrors the calls on
OAuth2TokenService::Observer::On{Start,End}BatchChanges.

Bug: 897113
Change-Id: I6a436baf28f4bf629da8a9b037cd5ab04c644fe1
Reviewed-on: https://chromium-review.googlesource.com/c/1296249
Commit-Queue: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603071}
3 files changed