Right now - if there's an error during DnsWriter.publish*, all the publish from
before that error will be committed, while all the publish after that error
will not.
More than that - in some writers partial publishes can be committed, depending
on implementation.
This defines a new contract that publish* are only committed when .commit is
called. That way any error will simply mean no publish is committed.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=165708063
d5ac03aae4