Migrate accounts_mutator_unittest.cc to public TestIdentityManagerObserver

Use the public class TestIdentityManagerObserver instead of the internal
implementation in accounts_mutator_unittest.cc, and migrate to using that
class' APIs to initially set |OnceClosure| callbacks inside the scope of
the test's RunLoop, to finally check the results via the public methods
provided by TestIdentityManagerObserver for that purpose.

Bug: 930192
Change-Id: Ia5329a0aedaf596a343e32f61b3c9c9bcf06d1ab
Reviewed-on: https://chromium-review.googlesource.com/c/1473275
Commit-Queue: Mario Sanchez Prada <mario@igalia.com>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#632584}
1 file changed