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A non-broken but recently broken QUIC alternative service does not race for 0RTT
(because it is recently broken) but is still used (because it is not broken).
Upon successful connection, the service should be confirmed (marked as not
recently broken so that it can be used next time for 0RTT).

This CL adds this functionality and a test for it.  I locally verified that the
test fails without the rest of the change.

BUG=392575

Review URL: https://codereview.chromium.org/1035713003

Cr-Commit-Position: refs/heads/master@{#322455}