Is it okay to just make Put's src parameter be []*proto.Message now? 

I'm not sure, I have to double-check the usage... That would be ideal though.

Nope, not yet. completed_builds and completed_steps do not use Messages yet. I'm going to make a bug for that.

https://bugs.chromium.org/p/chromium/issues/detail?id=791059

We're removing the build instrumentation from kitchen. Nodir, the current data that kitchen is reporting is incorrect, right? Should we just remove the instrumentation for builds from kitchen?

For steps, we're planning on keeping the instrumentation in kitchen, but replacing it with a new schema?   

yes, we should just remove it

for steps, we are going to pipe them to buildbucket and buildbucket will report them. in any case, kitchen will not send data to bq

I recommend ...*proto.Message instead of []*proto.Message.
...*proto.Message is easier to use if you have a constant number of events.

The following revision refers to this bug:
  https://chromium.googlesource.com/infra/infra/+/ec4bc5d5da3b1f4e54ef687454210193de7d8e31

commit ec4bc5d5da3b1f4e54ef687454210193de7d8e31
Author: Katie Thomas <katthomas@google.com>
Date: Tue Jan 23 18:36:49 2018

[kitchen] remove event sending

R=nodir@chromium.org

Bug:791032
Change-Id: Iac2c54a3ee306d1beda049bc3e00dabdbbc02a5b
Reviewed-on: https://chromium-review.googlesource.com/879383
Reviewed-by: Nodir Turakulov <nodir@chromium.org>
Commit-Queue: Katie Thomas <katthomas@google.com>

[modify] https://crrev.com/ec4bc5d5da3b1f4e54ef687454210193de7d8e31/go/src/infra/tools/kitchen/cook.go
[delete] https://crrev.com/991b18cdacfbf3f8a0b63605683ee1caf0def114/go/src/infra/tools/kitchen/monitoring.go
[delete] https://crrev.com/991b18cdacfbf3f8a0b63605683ee1caf0def114/go/src/infra/tools/kitchen/monitoring_test.go
[modify] https://crrev.com/ec4bc5d5da3b1f4e54ef687454210193de7d8e31/go/src/infra/tools/kitchen/cook_test.go