This also bypasses signed mark validation during domain creation if
the flow is being executed as superuser.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=145435268
This also fixes up a hook on the domain create flow custom logic to use a single
parameter, which is the general pattern we want to use going forward. It also
establishes a pattern for custom logic being able to add extensions.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=139362230