TransportCredentials are per-request, not per-session, and
there's no reason to carry them within SessionMetadata.
While I'm in here, get rid of "null" credentials.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=125202213
This introduces Actions and Dagger up until FlowRunner. The changes
to the servlets are relatively simple, but the required changes to
the tests, as well as to auxillary EPP endpoints (such as the http
check api and the load test servlet) were vast. I've added some
comments in critique to make the review easier that don't really
make sense as in-code comments for the future.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=124593546
