Fix methods related to OnRefreshTokenRemoved in TestIdentityManagerObserver

Small patch to provide a more consistent name for the method that returns
the |account_id| received by the observer via the |OnRefreshTokenRemoved|
callback, and to fix the signature of the RepeatingCallback passed to the
|SetOnRefreshTokenRemovedCallback| method so that now pass a |OnceClosure|
instead (should be enough), useful to migrate accounts_mutator_unittest.cc.

Note that the |std::string| parameter that existed in the previous signature
of that callback was really not needed since the id received when the
|OnRefreshTokenRemoved| callback gets triggered is saved at that moment,
and can be retrieved via |AccountFromRefreshTokenRemovedCallback|.

Bug: 930192
Change-Id: Ied8eedd45ef43a0ba0236cf6c8a8def5713ff731
Reviewed-on: https://chromium-review.googlesource.com/c/1473176
Commit-Queue: Mario Sanchez Prada <mario@igalia.com>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#632576}
3 files changed