Reenable SingleClientSessionsSyncTest.CookieJarMismatch

The test has been historically flaky but many things have changed since
the last reported flakes (in particular, migration of SESSIONS to USS)
so chances are that we no longer repro the flakes.

We also do some related code cleanup.

Bug: 789129
Change-Id: I7f70d8d0d1c96232ffe07197e8e1982759e8af02
Commit-Queue: Mikel Astiz <>
Reviewed-by: Marc Treib <>
Cr-Commit-Position: refs/heads/master@{#615138}
1 file changed